28 



HEREDITY AS ILLUSTRATED BY TRICHOMES. 



were sufficient to indicate that this is essentially different from the long 

 secreting 1 trichome of the other type. Fig'. 7, ,e, shows a cross-section of a 

 head which has reached the 5-celled stage. The fifth cell is formed by 

 the laying down of a radially placed wall by which the mother-cell is divided 

 unequally. In fig'. 7, ./', each of the 4 cells is divided by a radial wall, so 

 that the mature, or 8-celled, condition has resulted. 



FIG. ".Trichomes of Jiiyliinx niiirn: n to e, long secreting trichomes (, h, c, /I, and e X 585); 



/ to ./, long secreting triohomes of the typo having a head of more than 4 cells (/, </, and /*, 



;535; /and.) 84) ; k to /, short secreting trichomes, of which ?i to /-are from the region of the 



veins of the leaves and is from the leaf-margin (k, I, and , 1200 : m, n, p, //, r, s, and (, 



.%">). (Reduced one-flfth). 



In several trichomes the head was observed to be composed of 7 cells 

 only, but whether these were immature or not was not determined. From 

 a careful study of this type of trichome it would seem that 8 is the usual 

 number of cells in the head. No measurements were made on the length 

 of the heads, but the following numbers, in /*, give the diameter for the 

 type of trichome in question. The measurements were made only on 

 what were thought to be mature forms. Diameter of heads: 54.6, 50.4, 



