42 



HEREDITY AS ILLUSTRATED BY TRICHOMES. 



in its development were seen. Measurements on the mature trichomes 

 show that the variation in length of the entire organ, but particularly of the 

 head, is in some manner associated with the position occupied by it, as has 

 been repeatedly noted in other forms. And, also, as in the other similar 

 measurements, this variation was found to be in a high degree consistent, 

 which is indicated by the tables of measurements (tables 18 and 19). 



Table 18. Length of short secreting trichomes ofjuglans californica 

 X Juglans regia, F v ( Trichomes of old leaves.) 



The averages in length of trichomes are: dorsal surface, 45.5 M-; ventral, 

 28.2 /*. Similar results were obtained in another series of measurements, 

 which need not be given, in which the dorsally placed trichomes averaged 

 35.9 m and the ventrally placed ones 28.1 p in length. 



Table 19. Measurements on heads of short secreting trichomes of Juglans 

 californica X Juglans regia, F"^. (Trichomes of old leaves). 



The averages in length of the heads are: dorsal surface, 18.9 ^; ventral 

 surface 15.5m. 



JUGLANS HYBRIDS-SECOND GENERATION. 



The material for the study of the Juglans hybrids and their pure parents, 

 which has been reported on above, was collected in the spring of 1907. 

 This material, unless otherwise specifically noted, was of the first genera- 

 tion. The study was resumed in 1908 for the following purposes: It 

 seemed best to obtain trichomes which were undergoing nuclear division 

 in order to satisfactorily determine the sequence of the cell-divisions, and, 

 also, it seemed best to carry the study of the variation of the trichomes 

 somewhat further, and to learn if possible the relation between the vari- 

 ation of the trichomes and the variation of the plant bearing them. 



In selecting the plants for study it was decided to take 2 each of the 

 largest and the smallest of both kinds of hybrids. The largest Juglans 



