46 



HEREDITY AS ILLUSTRATED BY TRICHOMES. 



ones in the head-cells. The trichome then consists of a head of 4 cells, 

 radially disposed, and a stalk of 2 cells, and cell-division ceases. Although 

 numerous examples of each stag-e in the development of the trichome were 

 seen, no exception to the sequence as given was noted. 



The long secreting trichome in Juglans calif ornica X Juglans nigra is of 

 two sorts. One type has a stalk of 4 cells and a head of 4 cells, and the 



Fig. 12.— Long and short Sfcreting trichomes of Juglans californica X Juglans nigra, F2, plant 1: 

 a, third cell-division of trichome; b, 4-celled trichome, of which only 3 cells are shown; e, fourth 

 cell-division of trichome; d, flfth cell-division shown in transverse and longitudinal sec- 

 tions. (All figures X 1200.) 



Other type has a stalk of about 8 cells and a head of about 8 cells. The 

 development of the first kind is as follows: The first cell-division of the 

 young- trichome is transverse, by which the portion which is to become 

 the head is differentiated from the portion which is to become the support- 

 ing stalk. The second division is longitudinal in the head, the third is 



