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 stage in the development of the trichome were 

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



The long secreting trichome in Juglans calif arnica 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 secreting trichomes of Juglaius californica X Juglans nigra, F 2 , plant 1: 

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

 cell-division of trichome; d, fifth 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 

 yoimg 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 



