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THE AMERICAN NATURALIST [Vol. XLII 



2). Consequently it happens from this single initial de- 

 viation, there arises a form of trichome, unrelated to 

 other existing types, and, consequently, of which it can 

 in no wise he said to he a modification. In fact the new 

 hair is a mutation, and its history shows in at least one 

 way how such variation has its origin. In this instance 

 there is no disappearance of intermediate forms of tri- 

 chomes, since for structural reasons there can not be such. 



We therefore find in Juglans that the different types 

 of multicellular trichomes may take their origin in one 

 of two ways, namely, they may arise as modifications of 

 types already existing in the plant, which is apparently 

 the usual manner, or they may arise suddenly and hence 

 provide points of departure for subsequent trichome 

 formation and differentiation of which they would be the 

 ancestral type. 



The physiological reasons for the differentiation of the 

 trichomes were not investigated, but observations indi- 

 cate a close relation between size of hair and the position 

 occupied by it on the plant member, and suggest that the 

 factor of nutrition may be important in inducing certain, 

 at least, of the irregularities noted. 



