HYBRIDS OF JUGLANS. 



45 



although the head consisted of 6 cells only. It is thought that there may 

 be a relation between the large number of cells of which the mature tri- 

 chome is composed and the lack of consistency in the sequence of its cell- 

 divisions. The head of the mature disk-shaped trichome is composed of 

 at least 32 cells. 



PIG. 11. Trlchomes ofJuylans californica X J> nigra, F 2 , plant No. 1: a, figures 

 showing the cutting off of the young trichome from the epidermis of the 

 leaf; b, first cell-division of trichome; c, second or longitudinal division of tri- 

 chome. (All figures X 1200.) 



As opposed to the want of uniformity in the cell-division sequence shown 

 in the disk-shaped trichome, the divisions in the short and the long 

 secreting trichomes follow a perfectly consistent sequence throughout. 

 After the short secreting trichome is cut off from the epidermis it under- 

 goes division by a transverse wall into a terminal cell, which will give rise 

 to the head, and a basal portion, the stalk. The second division occurs in 

 the end-cell and is a longitudinal one. The third division of the trichome 

 is a transverse one in the stalk, by which the divisions in the stalk region 

 are completed. The fourth and the fifth cell-divisions are longitudinal 



