26 



HEREDITY AS ILLUSTRATED BY TRICHOMES. 



In table 8 the figures in the rig'ht-hand columns are the depths of the 

 depressions of the trichomes whose diameters are given in the correspond- 

 ing lines in the left-hand columns. 



The averag'e diameter of the heads of the disk-shaped trichomes is 77.5 M; 

 the average depth of the depression of the heads is 25.0 /*. Reference to 

 the measurements on the disk-shaped trichomes in /u^/ans calif ornica, given 



Fi(3. I). Trichomes of Jttf/ltiitx nigru: a, awn -shaped trichome (ca., 242 H)\ l> to/;, development of 

 disk-shaped triehomes (/*, c, d, e, /, /, and/-, ,o3f): (/, h t and ./, .- N4j; Mo </, stages in devel- 

 opment of lone secreting tricboines ( ."A") : / 1200). (Reduced one-tin.li). 



at page 21, will show that those of Jnglans nigra are noticeably smaller, 

 but the structure and the development, so far as known, of the two species 

 is the same. 



The long secreting trichomes are of two types, of which one has a head 

 of 4 cells, and the other a head of about 8 cells. Of these the former will 

 be described first. The trichome is 100 M to 150 p in length (fig. 7, a to e). 



