A Progeny Tes orf Douglas-Fir

RRITISH CD1,UIWBIA FOREST 5ERVICE A Progeny Tes orf Douglas-Fir portance of Selection Forest Practice FOREST SERVICE DEPARTMENT OF LANDS, FORESTS, AND WATE RESOURCES

ERRATUM Statistics for Clone No. 20, Table 7: page 14, Research Note No. 43, should read as follows :." 7"" 1 Clone No. LO

a* A PROGENY TEST OF DOUGLAS-FIR TO DEMONSTRATE THE IMPORTANCE OF SELECTION IN REFORESTATION PRACTICE by A. L. Orr-Ewing

ABS TR AC T The objective of this study was to demonstrate that much of the phenotypic variation in young stands of Douglas-fir was inherent and, consequently, of importance in reforestation practice. For this reason, several trees with widely different forms were selected in 1954 and their open-pollinated cones picked to initiate half- sib progeny tests. Scions also were collected for propagation. An assessment of both heights and forms of the different progenies was made on completion of their twelfth growing season. It was found that there had been some significant changes in the ranking of the respective progenies from the nursery measurements made at the end of the third growing season. In general, the trees selected for their better qualities had produced the tallest and best formed pro genies. These results emphasise the necessity for careful supervision and selection in routine cone collections. The value of a half- sib progeny test and the importance of replication in several environments were most apparent from this study.

~.l. l_.._._._..._._._..--...-- TABLE OF CONTENTS V8W 3E7 Page ABSTRACT IN T R 0 D UC T ION... ~.- 1 SELECTION OF THE PARENT TREES AND CONE COLLECTIONS.. -.. 1 PLANTING AND LATER DEVELOPMENT OF THE PROGENIES- 7 GRAFTING AND LATER DEVELOPMENT OF THE CLONES- 13 ASSESSMENT OF STEM FORM IN THE PROGENIES AND CLONES- 15 Plate 1 LIST OF ILLUSTRATIONS Tree 13. Selected for good features. 2 Tree 21. Selected for undesirable features. 3 4 Class 1. Straight. Class 2. Crooks, small, 1-2. 5 Class 3. Crooks, small, 3 or more. 6 7 8 9 10 11 12 Class 4. Crooks, pronounced, 1-2. Class 4. Concealed crook, low on stem. Class 5. Crooks, pronounced, 3 or more. Tree 17. Selected.1954. Left, clone (arrow). Right, progeny, 1965. Tree 19. Selected,1954. Left, clone (arrow). Right, progeny, 1965.

INTRODUCTION There is an unusual amount of phenotypic' variation in young natural stands of coastal Douglas-fir. This is particularly evident in open-grown stands which are those most favoured for the collection cones. It is comparatively easy to select trees which differ widely in such features as crown form, stem straightness, and the angle, length and thickness of the branches. In a seed production area, the trees with the most undesirable features should have been removed, but this is not the case in routine cone collections made in unimproved stands. of There is also little or no prior selection of the parent trees and the natural tendency, particularly in the case of cone collecting by contract, is to collect from those trees which can be the most readily climbed. These, however, are often the less desirable trees in the stand. It was felt that the only way to demonstrate the vital need for some selection standards in such stands was to collect cones from trees with widely different characters and compare the subsequent development of their progenies by properly replicated tests. In addition, scions should be grafted from each of the trees because the clones would indicate whether the desirable and undesirable features were inherent. U In consideration of these factors, a study was initiated in 1954. The main objectives now having been fulfilled, it is felt that wider circulation of the results is justified. SELECTION OF THE PARENT TREES AND CONE COLLECTIONS A flat area: three miles south of the Forest Experiment Station at Lake Cowichan, was selected for the study. It was at an elevation of 650 feet and had been logged and burned in 1925. Natural restocking had been slow with the result that the Douglas-fir were open-grown and had ample space in which to develop. Because there was a great deal of phenotypic variation in this stand, the writer had no difficulty in selecting 12 trees over an area of less than 200 acres. Six of the trees, numbered from 13 to 18, were selected for their straight stems, narrow crowns, thin branching habit, and good growth. The remaining six, numbering from 19to 24, were selected purposely for such undesirable features as crooked stems, wide crowns, and heavy branching. The location of these 12 trees is shown in Map 1. f Individuals described on the basis of demonstrable characters. Similar phenotypes do not necessarily breed alike (Snyder, 1959).

- 2- The selection criteria were not as strict as those used in the later cruises for plus trees (Orr-Ewing 1957) because no comparative measurements were made with surrounding trees. In addition, each selected tree had to have sufficient cones to provide enough seed for the progeny tests. This automatically excluded a number of potential candidates as the cone crop was by no means general in 1954. As is evident from Plates 1 and 2, however, there was little difficulty in selecting trees with'widely different habits of growth. Cones were collected from each of the trees in early September and it was not without significance that Trees 13 to 18 were much more difficult to climb to collect cones from than Trees 19 to 24. Table 1 gives the heights, diameters at breast height, and ages of the 12 trees, together with details on the number of cones collected and the yield of cleaned seed. Because there was a lot of insect damage to the cones on some trees, as many cones as possible were collected from each of them. As can be seen from the table, the amount of seed obtained after cleaning varied considerably.

- 3 - W e 18 23 SCALE: I INCH TO 6 CHAINS Map 1. Location of the selected trees.

~ - 4- Table 1. The selected Trees 13 to 18 and 19 to 24 with data on the cone collections. I: Tree Age at B. Ht. Height in* F t. * D. B. H. in. Inches No. of Cones Collected =F No. of Cleanec Seeds No. of Cleaned Seeds per Cone 13 21 68 11. 8 21 87 1 41. 5 14 23 63 14. 0 170 5979 35. 2 15 19 55 10. 6 178 3 067 17. 2 16 18 61 13. 9 122 2715 22. 3 17 24 74 16. 7 47 1877 39.9 18 19 63 12. 6 106 29 53 27.9 19 20 58 14. 0 52 1102 21. 2 20 24 59 18. 5 25 2 4162 16. 5 21 27 55 15. 8 36 57 8 16. 1 22 24 53 14. 5 1 57 24 2 1.5 23 26 56 18. 4 165 3 670 22. 2 24 26 73 19. 3 3 86 2817 7.3 L k Measurements made August 1956.

- 5- NURSERY RESULTS Each of the 12 seed lots was stratified and sown broadcast in two replicated beds at the nursery in May 1955, the position of each seed lot being selected at random. No germination counts were made, but at the end of the second growing season, in 1956, there were only 17 surviving seedlings from Tree 22 so they have not been included in any further analysis. Twenty seedlings from the remaining 11 parents were then measured in inches in each of the two replications, every "nth" one being measured dependent on the total number in the bed. The following April, 200 seedlings representative of each parent tree (with the exception of those from Tree 19 where only 86 were available) were mechanically selected prior to being lifted and transplanted into two replicated beds. The positions of the 11 progenies in each of the two beds were again assigned at random. At the end of the third growing season in 1958, the heights of20 seedlings per parent tree were measured in each of the two replications, the criteria being identical to those used the previous year. The results of these nursery measurements have been summarized in Table 2 and show the ranking of the 11 progenies. It was found that the heights of the progeny from Tree 19, a most undesirable phenotype: were significantly taller than all the other progenies with the exception of those from Tree 14 in 1956, and from Tree 15 in 1957. On the other hand, in 1957, the heights of the progeny from Tree 24, another poor phenotype, were already significantly less than six of the other pro genies.

-6- Table 2. Summary of the mean heights of the progenies ranked by years in the nursery. 1956, 2tO years 1957, 2+ 1 years Pro g eny No. Measured vlean Ht. in Inches S.E. of Mean Progeny No. vleasured Mean Ht. in Inches S. E. of Mean 19~~::: 40 9.6.37 19XW 40 17. 1.69 14XW II 8.7. 51 15xw I1 15. 2. 81 2lXW I1 7.8.32 21 xw 11 15. 0 e 56 13xw I1 7.3. 25 14XW It 14. 8.72 15xw I1 7.3.36 17XW 11 13.9.67 17XW 11 7.2.38 18XW I1 13.6 c 59 24xw II 6.9.31 13XW 11 13.0.62 16XW I1 6. 5.34 23XW II 12. 8. 50 c 18XW 23xw II II 6. 5 6. 5. 24. 24 20xw 16XW II II 12.7 12.2. 53.60 20xw II 6.4.30 24XW 11 11.8.45 : W signifies wind-pollination, in other words, the pollen parent was not known.

- 7. - PLANTING AND LATER DEVELOPMENT OF THE PROGENIES The survival of the 11 progenies in the transplant beds was extremely good and in no instance dropped below 93 per cent. In March 1958, every fourth seedling in each replication of the progenies was marked for planting on a level area at the Forest Experiment Station at Lake Cowichan (elevation 800 feet). These 48 seedlings from each of the 11 parent trees were then lifted and planted in rows at 8 by 12 foot spacing in four replications, their position in each being assigned at random. The four replications were all within 1, 200 feet of each other and on relatively flat ground. Every planted seedling was protected against browsing by wire cages which were later removed once a deer fence had been built around the whole area. At least 90 seedlings from 10 of the parent trees were next selected in similar fashion at the nursery, lifted and then planted in rows in three replicated blocks in the Robertson Valley eight miles south at an elevation of 800 feet. The only exception to this procedure were the 31 remaining seedlings from Tree 19 which were planted but not replicated. There were still enough seedlings remaining at the nursery for an unreplicated planting at Nineteen Creek, three miles southwest of the Experiment Station at an elevation of 1, 100 feet. url Table 3 shows the total number of progenies planted together with survival at the Forest Experiment Station and Nineteen Creek plantations. No figures, however, have been included for the Robertson Valley plantation as it has been so badly damaged by repeated frosts that no analysis can be made at this time. In general, survival at the first two plantations has been satisfactory, almost all the losses being from root rot. The Nineteen Creek plantation, however, was heavily browsed by deer after establishment but is now growing well. The heights of the progenies on the Forest Experiment Station were measured in 1959, 1962, 1963, 1965, and 1966. Table 4 summarizes the results of those made in 1959, 1963, and 1966. It is evident that there have been some major changes from the nursery rankings in 1957. The progeny from Tree 13, in particular, which were only ranked seventh in the nursery, are now the tallest and, moreover, significantly taller than five of the other 10 progenies. On the other hand, the progeny from Tree 19, which were the tallest both in the nursery and in the year following planting, are now ranked third. The progeny from Tree 21, again, which were ranked third in the nursery have now dropped to eighth place. The only progenies which have consistently remained in the lowest positions are those from Trees 16, 18, and 24. W

- 8 - The importance of replication within a planting area is shown in Table 5 which summarizes the ranking mean heights of these progenies in each replication. As mentioned previously, the summarized heights for all four replications in Table 4 shows that the progeny from Tree 21 are only ranked in eighth place. The ranking by replication is eleventh, eighth, first and eighth. The high ranking in the third replication, however, can be easily explained as the progeny are particularly favoured by growing in a location with abundant moisture. The importance of progeny testing on more than one planting area is also indicated in Table 6 which shows the average heights of the progenies at Nineteen Creek. These trees had been planted in unreplicated lines at 8- by 8-foot spacing on a steep slope with a southerly aspect. The heights of all the progenies are significantly less than those at the Forest Experiment Station, but this could have been largely influenced by browsing. It is, however, of interest to find that the poorest progenies at the Forest Experiment Station, namely those from Trees 16, 18 and 24, are still among the poorest at Nineteen Creek, On the other hand, the progeny from Tree 13 which were the tallest at the Forest Experiment Station, are now only ranked sixth. It might be questioned whether any estimates of heritability for height growth had been obtained from these progenies. Some estimates have been made but purposely have not been included in this paper. Stonecypher (1966) recently reviewed past estimates of heritability and observed that those made for forest tree populations and obtained from a small number of families grown in single environments are, in general, very unreliable. Many of the published heritability estimates further should be viewed with caution as few of the studies from which the estimates have been made were originally designed to estimate genetic variances. This study was not originally designed for such estimations and accordingly there seems little point in publishing unreliable data. I'

- 9 - U Table 3. Total number of seedlings planted and their survival in two plantations, 1966.

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- 12- Table 6. Summary of the mean heights of the progenies ranked by years at Nineteen Creek. 1963 1966 Progeny No. Measured dean Ht. in Ft. S.E. of Mean Progeny No. Measured Mean Ht, in Ft. S.E. of Mean 15xw 17XW 14XW 20xw 39 39 33 37 7. 8 7. 5 7.1 7.0. 26. 21. 24. 25 17XW 15XW 20x w 21xw 35 39 36 37 14. 4 14. 1 13. 2 13. 1. 27.35.38.35 21xw 16XW 18XW 13xw 39 37 38 40 7. 0 6. 8 6. 6 6. 5. 2 4. 20. 22 * 21 14XW 13xw 16XW 18XW 29 36 36 35 13. 0 12.9 12.9 12. 8.31. 28. 27.31,* 23XW 38 6. 5. 26 23xw 35 12.0. 26 24x w 39 5. 7.19 24x w 39 10. 8.41

- 13 - GRAFTING AND LATER DEVELOPMENT OF THE CLONES:: As mentioned in earlier pages, it had been decided that scions would be removed from each of the selected trees and the clones established in order to determine whether the variations in form of the different trees were inherent. In March 1956, therefore, scions were collected from the tops of each of the trees. They were then brought into a greenhouse and grafted by the side veneer method to two-year-old rootstock of Cowichan origin which had been potted in 1955. In June 1956, the ramets** were repotted in larger containers and planted in the nursery. The following March, these clones were planted adjacent to the rows of each of the respective progenies which were to be planted the next year. Thus, in all four replications, there were adjacent rows of clone and progenies for each of the selected trees, 1y' The summarized results from grafting to the survival of the 11 clones in 1966 are given in Table 7. It is evident that there has been high mortality among some clones. Much of this occurred during the two summers following planting when the weather was very dry. Mortality after 1963, however, has been entirely due to either root rot or the overgrowth of scion to rootstock. Some of the ramets, in particular those of Clone 14, have grown extremely fast but it is considered that any further analysis is meaningless as only eight of the clones are represented in all four replications. There is also the effect of incipient overgrowth on some ramets. Indeed, as Schrock (1965) has pointed out, comparisons between clonal material are onlv valid if thev are grafted on geneticallv identical material. The few ramets Der clone that have survived, however, do convincingly demonstrate that much of the variability shown in the 11 parent trees is undoubtedly inherent. * Clone. A group of plants derived from a single individual by asexual reproduction (Snyder 1959). *<* Ramet. An individual member of a clone (Snyder 1959). W

- 14 - Table 7. Summary of survival and subsequent development of the clones. c

- 15 - w ASSESSMENT OF STEM FORM IN THE PROGENIES AND CLONES Stem form is a difficult character to assess but it was felt the height records of these progenies should be supplemented by some measure of their form. As Goddard et a1 (1964) have pointed out, bole sweep, crook, and twist were serious defects which could cause substantial losses in volume and value. They added, further, that as a result of the economic importance of bole straightness, this feature was often weighted as much or more than any other in single tree selection. In regard to the assessment of stem form, Keiding et a1 (1965) have pointed out that there were three main methods, firstly by evaluation on the basis of measurements: secondly by scoring, and thirdly by both measurements and scoring. Goddard et a1 (1964) considered the main disadvantage to the second method was that there were no "quantitative" measurements for such factors as crooks. This is certainly correct but, on the other hand, scoring is much the faster method when many progenies are concerned and is probably just as accurate when carried out by personnel with detailed knowledge of their past history. Keiding et a1 11965) have used the scoring system alone for assessing stem form in the clones and progenies of larch. Their material was divided into five distinct classes, each of which was illustrated with type trees. These classes were listed as follows: Class 1. Absolutely straight without any crooks. Class 2. Small crooks, one to two in number. Class 3. Small crooks, three or more in number. Class 4. Pronounced crooks, one to two in number. Class 5. Pronounced crooks, three or more in number. They further emphasized the importance of distinguishing between small and pronounced crooks, the former being considered of only minor important to the quality of the stem, Their system appeared the most suitable for scoring the progenies in this study but a few small changes were first made. Firstly, a crook was only defined as pronounced when it had an estimated offset of more than one and a half inches. Secondly, forked trees with two or more leaders for at least two growing seasons were included in Class 4. Thirdly, trees with double stems from ground level were included in Class 5 as this was considered a most undesirable character. At each of the four examinations of these progenies in previous

- 16 - years, particular attention had been given to leader damage and to those trees with double stems. The latter condition had been particularly evident in 1959 and was largely due to frost damage in the nursery. It had., however; only persisted in a few trees. A final modification to the system was that the trees were only scored in one class., the scoring of a tree by fractions into several classes as used by Keiding et a1 ( 1965) was not found necessary. ''W The progenies and clones at the Forest Experiment Station were duly assessed in person on three separate dates in 1966, the results of each examination being compared to determine whether there had been any major differences in the scoring. None was found. The scoring was conducted with great care, each tree was viewed from all angles and particular attention was paid to those with dense foliage which could obscure crooks low on the stem. Type trees illustrating each of the classes are shown in Plates 3 to 8. The results have been summarized in Table 8 and demonstrate that five of the six trees selected for desirable features have produced progenies with better form than the remainder. It is recognized that at this age a number of those trees scored for severe crook may not show it when they reach merchantable size for sawtimber as these undesirable features will then be masked. As Barber i1964) has pointed out, however, even if these crooks are masked when the tree has reached a large diameter, it does not correct the poor-quality wood now being produced. Compression wood formed at young ages remains compression wood with subsequent degrading in lumber and reduction of pulp strength. In spite of the variable numbers and missing replications, an assessment was also made of the 11 clones. The results shown in Table 9 demonstrate that the poor forms of Trees 19, 20, and 24, in particular, are undoubtedly inherent. The majority of the clones from the trees selected for their better form are again ranked higher, although their scorings were confined to Class 3 and lower. The amount of crook in some of the clones from the better trees would indicate that the selection standards for stem straightness in the original trees could have been improved. Tree 16, in particular, was a poor selection for both growth and form. The variability in form within a clone such as in Clone 17 was also of interest. This has been also noted by Keiding et a1 11965) in their assessment of larch clones. They considered that some clones were less stable than others and were more easily influenced by smaller changes in the environment.

- 17 - There can be no denying, however, that real genotypic*c differences do exist between the parent trees selected and, moreover, that these can be transmitted to their progenies. This can be readily illustrated by Plates 9 to 12. Plate 9 shows Tree 17 in 1954. This tree was selected for its narrow crown, thin branching, rapid growth and relatively straight stem. Plate 10 shows, on the left, the clone and, on the right, the row of progeny from this tree in 1965. The good form and rapid growth of both clone and progeny needs no further comment. Plate 11, on the other hand, shows Tree 19 in 1954. This tree which is only half a mile from Tree 17 was selected for its particularly bad form, Plate 12, photographed in 1965, shows on the left the clone which clearly indicates that the bad form is inherent. The progeny, however, are of more practical interest as there is a preponderance of severe crook, although they are vigorous and in 1966 were ranked third in height growth. It may be argued that Tree 1.9 is an exception to the usual type of tree found growing in cone collection areas. This is not the case as even worse examples have been found without any difficulty since this study was initiated. An attempt was also made to score the progenies at Nineteen Creek but the trees were still too small. 96 Genotype. An individual' s hereditary constitution and determined chiefly from breeding behaviour (Snyder 1959).

- 18 - Table 8. Summary of the ranked scoring for form of the progenies, 1966. L Progeny No. of Trees Scored I Form Class If fii "- v 18 42 15 15 10 1 1 17 46 10 21 12 3 14 47 7 16 14 8 2 13 45 5 15 21 4 15 46 4 16 17 7 2 21 47 3 11 18 14 1 24 48 1 12 19 12 4 'J* 16 45 12 15 14 4 20 48 8 26 13 1 23 43 8 19 11 5 19 43 1 18 14 10

-19 - U Table 9. Summary of the ranked scoring for form of the clones, 1966. Clone No. of Ramets Scored I Form Class 111 IV V 14 8 1 18 12 5 1 21 5 1 17 9 5 2 13 3 2 15 12 6 5 23 3 1 2 16 8 1 7 19 1 1 20 1 1 24 1 12 4 12 12 4 12

- 20 - DISCUSSION 'I" This study was the first attempt made at selection and at grafting selected Douglas-fir in British Columbia. Although the study could doubtlessly have been improved, the original objectives have largely been fulfilled. Two of the progenies from the six trees selected for their desirable features are now ranked first and second in height growth at the Forest Experiment Station, while another two are ranked fifth and sixth. At the unreplicated planting at Nineteen Creek,. the same four progenies although ranked differently, are also growing well. Only the performance to date of two of these six progenies; namely from Trees 16 and 18, have been disappointing, although the latter progeny are ranked first for form. On the other hand, only two of the five progenies from the trees selected for undesirable features are included in the first six rankings for height growth at the Forest Experiment Station. These rankings are no higher at Nineteen Creek. In regard to the assessment of form, three of bhese five progenies are ranked the lowest while even the best is ranked no higher than sixth. There may well be further changes among the progenies as regards height growth, but the assessment for form has probably been scored at the most appropriate time. As Keiding et a1 (1965) have pointed out, 'scoring for stem form seems dependent on the age of the tree and the evaluation might be best conducted when crookedness is at its worst; that is. between the 5th and the 20th year. ' v. These results can only emphasize the necessity for supervision and selection in all unimproved stands of Douglas-fir and indeed of other species. The time spent on selection in the manner described in this study is negligible compared with that spent in growing the seedlings to rotation age. Some valuable lessons for future progeny testing have also been learned from this study. Firstly, a great deal of useful information on the general combining ability of selected trees can be obtained by half-sib::: progeny tests. Full-sib tests where both parents are known will certainly yield more information but progress is slower as it is hardly possible to carry out extensive pollinations on the trees themselves. This is particularly true when the trees are the size and in the locations of those selected in the present plus tree program. Such trees must first be grafted and the clone well established before cones and pollen are produced in sufficient numbers. In addition, the clone may succumb to overgrowth before any cones are produced. In the meantime, wind-pollinated cones could have been collected in a good cone year for the half-sib progeny tests which should indicate which : Half-sib. Progenies with only one parent in common (Snyder, 1959).

- 21 - U selections will give superior progeny when pollinated by other trees. This knowledge will be of real value to the breeder when selecting clones for subsequent full-sib tests. It is of interest to note that four of the trees selected for this study have since been used for full-sib crosses. The development of their progenies to date, further endorses these conclusions. Secondly, the changes in height-ranking of some of the progenies in this study, from the nursery to their development on planting areas nine years later, emphasizes the need for caution in basing conclusions on early results in the nursery. There is no question that testing must be continued on several selected planting areas. However, it is felt that, provided damage and mortality from environmental factors can be kept to a minimum, progeny tests, simil.ar to those described in this study, can yield enough information at 12 to 15 years after planting for at least the poorer progenies to be recognized and culled. There already is sufficient evidence from this study for deciding which of the trees selected for desirable features should be accepted or rejected. Finally: some aspects of the importance of experimental design in progeny testing have been demonstrated in this study. The need for replication within any one planting area and the necessity for testing in more than one environment has already been discussed. These factors were originally recognized in this study but no analysis could be made in the Robertson Valley plantation owing to repeated damage by frost. As a result, some valuable information has been lo st. It is hardly possible to envisage all the situations which can arise during the course of a progeny test, but damage by frost can be largely avoided by not planting valley bottoms. Browsing damage can also be very serious but it is much more difficult to control because the cost of fencing numerous plantations would be prohibitive. The only recourse is to avoid planting areas where there are known to be heavy winter populations of deer and where there has been heavy browsing in existing regeneration. V The method adopted of planting in rows in each replication inevitably limits the length of time the test can be continued. However, it is felt that, at this stage of development in genetics research, tests longer than from 12 to 15 years in duration are hardly justified. Much valuable information can be gained in this short period which can be used for planning further tests. From past experience: however, it is recommended that the number of seedlings representing each progeny on every planting area should be increased to at least one hundred. In addition to damage by frost and browsing, mortality from root rot can be very serious in some locoations. In another study, for example, which was planted at the Forest Experiment Station in 1958, there has already been 20 per cent mortality from root rot. This undoubtedly will increase because the sources of infection--the old stumps which are distributed throughout the plantation--cannot be removed. Such heavy mortality from one source alone can seriously limit the value of a test especially when only minimum numbers of seedlings are used.

- 22 - ACKNOWLEDGMENTS The advice of Mr. A. R. Fraser, Research Division, on both the design of this study and the analysis of the data is gratefully acknowledged, Mr. E. J. Chatelle, Federal Department Rural Development, kindly prepared the photographs. of Forestry and

- 23 - REFERENCES Barber, J. C., 1964. Inherent variation among slash pine progenies at the Ida Cason Callaway Foundation. U. S. Forest Serv. Res. Paper SE- 10, 90 p. Goddard, R. E. and R. K. Strickland, 1964. Crooked stem form in Loblolly pine. Silv. Genet. 13, 155-157. Keiding, H. and H. C. Olsen, 1965. Assessment of stem form in clones and progenies of Larch. Silv. Genet. 14; 115-122. Orr-Ewing, A. L., 1957. Selection of plus trees for seed orchards, B. C. For. Serv. Unpubl. M.S., 15 p. Schrock, 0., 1965. Der Einfluss von Reis und Unterlage auf Wuchsleistung und Wachtumsgang bei Kiefernpfropflingen (Pinusilvestris). Tagunsber. dtsch. Akad. Landwirtschaftsw. Berlin : 69 :37-66. W Snyder, E. B., 1959. Glossary for forest tree improvement workers. South, For. Expt. Stat. 22 p. Stonecypher, R. W., 1966. The Loblolly pine heritability study. Southlands Exp. Forest, Georgia. Tech. Bull. 5, 128 p.

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