Feb. ij. I9I5 Brachysm 391 



that normally produce the fruiting branches. The regular abortion of 

 these axillary buds renders it the more probable that the abortion of the 

 terminal bud was not accidental. The case shown on the left-hand figure 

 of Plate LXII, the transformation of the terminal bud into a flower bud 

 subtended by an abnormal leaf, affords still more definite evidence of 

 abnormality. 



SHORTENING OF INTERNODES BY DROUGHT 



The intemodes are always longer under conditions that favor luxuriant 

 growth of the plants than where growth is restricted by drought. Though 

 this relation is general, some varieties shorten their intemodes much 

 more than others. The susceptibility to shortening is sometimes so great 

 that the same variety may be short-jointed like a cluster cotton in some 

 places, while under other conditions it behaves as a normal long-jointed 

 variety. Attention was called some years ago to a case of this kind in a 

 variety called the Parker that had been grown in Texas for several 

 seasons as a long- jointed variety, but behaved as a short-jointed or semi- 

 cluster variety at Del Rio in the season of 1907.' 



The difference between the true brachysm and this false brachysm 

 induced by changes of external conditions is that the latter is not inher- 

 ited. The false brachysm represents an adaptive change or accommoda- 

 tion to the conditions instead of a definite alteration of the expression 

 relations of the characters. When whole stocks of plants or animals 

 respond in the same way to a change of external conditions, the changes 

 are usually in the nature of accommodations and are readily reversible. 

 But the possibility that an increase in the number of heritable varia- 

 tions toward brachysm might be induced by environmental shortening 

 of the fruiting branches would be worthy of investigation. This possi- 

 bility is suggested by the fact that individual variations in the direction 

 of the cluster habit appear more frequently in some locahties than in 

 others in the same variety of cotton. Thus, it was noticed in the season 

 of 1 9 13 that plants of the cluster fonn were of frequent occurrence in 

 many fields of Durango cotton in the Imperial Valley of California, 

 whereas in a field of Durango cotton at Deep Creek, Va., no cluster 

 plants could be found. 



Other illustrations of the influence of external conditions are afforded 

 by irregularities in the lengths of the intemodes of the same plant, or 

 even of the same branch. (See PI. LVII and LVIII.) In such cases the 



* " The Parker variety of cotton showed a pronouuced semiclustcr habit or shortcuiug of the internodes 

 of the fruit branches, a notable departure from the previous behavior of our stock of lliis variety, which 

 had been under observation in several different localities in the preceding years. Apart from the fact 

 tliat every precaution is taken to avoid mistakes in labeling and planting the seed, the possibility of error 

 in tliis case seems to be entirely eliminated by tlie fact that six different selections of Parker were grown 

 at Del Rio and that all of them behaved in the same manner with reference to this change in the lengths 

 of the fruiting branches. Plantings of the same strains from the same lots of seeds in several other localities 

 in Texas in the same season produced no such results." Cook, O. F. Suppressed and intensified cbarac- 

 ersin cotton hybrids. U. S. Dept. Agr. Bur. Plant Indus. Rul. 147. p. 30. 1909. 



