In the literature somewhat conflicting reports are found as to whether or not curliness will show up early in the growth of a tree or late. Apparently it was possible to trace curly grain into the twigs a few years old in the original Lamb walnut (unpublished letters). Various statements, however, indicate that curliness may not develop until the trees are 20 years old or more. It would seem that with the propagation and introduction of the Lamb walnut in 1926-27 and distribution soon thereafter it ought to be possible to locate and examine these trees which are now more than 20 years old.
[Illustration: Fig. 4. Slightly enlarged photograph of black walnut with straight grain in the wood (light-colored area) and also in the bark (dark-colored area). U. S. Forest Service Forest Products Laboratory Photo.]
In the various literature and other material available on the subject of birdseye and curliness, it appears that the birdseye grain is different in its origin from curliness although both may be related to the functioning of the cambium and definitely seem to be related to slow growth. (Ref. 8)
[Illustration: Fig. 5. Slightly enlarged photograph of black walnut with curly grain in the wood (light-colored area, upper left) and also in the bark (dark-colored area). U. S. Forest Service Forest Products Laboratory Photo.]
Curliness is reported in other kinds of trees. Curly grained white poplar has been propagated from hybrid trees by growing cuttings of shoots from the roots of the curly trees (Ref. 9). In Sweden it has been possible to grow figured birch, much of which has the curly type grain. In birch, seedling strains producing curly grain have been developed and are being grown. It is of interest to note that with these birches, the trees with curly grain grow only about half as fast as the normal trees and have to be staked during their early growth years in order to make straight trunks or to stand erect (Ref. 4).
The original Lamb walnut tree was curly throughout. Other trees, particularly maples and birches may be curly only in part of their trunks and sometimes only in restricted segments. Trees frequently have curly grain at the base where the trunk joins the roots but not elsewhere. Such curliness may be related to the shortening of the curve where the root joins the trunk, thus causing distortion. W. G. Bixby states (Ref. 3) that a birdseye maple tree 170 years old was only about a quarter as large in diameter as normal trees of the same age. I know of no comparison of curly walnut with other types of walnut. The original Lamb walnut tree was apparently a very large one.
In conclusion, it is obvious that our knowledge of the possibility of producing curly grained walnut logs by grafting is as yet incomplete. Much more information is needed and at the present time undoubtedly much can be gained by examining the Lamb walnut trees, which are growing in various parts of the country. This can be done without seriously injuring the trees as described earlier in this paper. Those in the Northern Nut Grower's Association, who have Lamb trees are urged to examine them to find out if we can gain further useful information regarding this rather important subject. Obviously, if it is possible to grow curly walnut through vegetative propagation, we should know under what conditions a grower can expect to successfully produce a curly grained log.
References
1. MacDaniels, L. H. The apple tree crotch, histological studies and
practical considerations. Cornell Univ. Agr. Exp. Sta. Bul. 419:
1-22. 1923.
2. —— and Otis F. Curtis. The effect of spiral ringing on solute
translocation on the structure of the regenerated tissue of the
apple. Cornell Univ. Agr. Exp. Sta. Memoir 133:1-32. 1930.