28 



HEREDITY AS ILLUSTRATED BY TRICHOMES. 



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

 secreting trichome of the other type. Fig. 7, g, 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. 7. Trichomes of Juglans nigra: a to e, long secreting trichomes (a, b, c, d, and e .; 535) ; 



/ to j, long secreting trichomes of the type having a heart of more than 4 cells ( /, (/, and ft, 



">:S5; i andj 84) ; k to t, short secreting trichomes, of which /i to care from the region of the 



veins of the leaves and * is from the leaf-margin (k, I, anrt o, 1200; m, n,p, (/, r, s, and /. 



535). (Reduced one-fifth). 



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, 



