60 HEREDITY AS ILLUSTRATED BY TRICHOMES. 



a trichomal system should not be taken together as a single unit, but should 

 be separated into as many units as there are trichome types.* 



The hybrid plants of the second generation which were taken for study 

 were among the largest and among the smallest of all of this generation, 

 and all were of the same age and apparently had had an equal chance in life. 

 The opportunity was thus given to observe the relation between vigor of the 

 plants as a whole and the size of the trichomes which they bore. The 

 results are contradictory, and because of this fact the value of the trichome 

 in a study of this character is shown to be great, as it probably is less 

 influenced by conditions attending general plant development than other 

 organic systems of the plant. The disk-shaped trichomes, and the short 

 secreting trichomes also, of plant 4 were somewhat larger than those in 

 the larger plant numbered 1 of the hybrid /w^/aw calif ornica X Juglans- 

 nigra, while these trichomes in plant A and in plant C of the other hybrid, 

 like and like, were practically of the same size. 



*See page ii. 



