HYBRIDS Ol : JUOLANS. 53 



are of diameters only; it was found not practicable to make a special 

 study of the depth of the head. Disk-shaped trichomes from No. 4, 

 diameters of heads: 79.8, 84, 84, 79.8, 92.4, 100.8, 71.4; the average 

 diameter is 84.6. The following are the diameters of disk-shaped tri- 

 chomes from No. 1: 84, 79.8, 79.8, 84, 84, 79.8, 79.8, 79.8, 71.4, 84, 79.8, 

 71.4; the average is 79.8. The disk-shaped trichomes from the smaller 

 plant, No. 4, average larger than those from the larger one, No. 1. In 

 both instances the trichomes run smaller than in the first generation 

 (101.1 /J-), and also smaller than in the pure species Juglans calif arnica 

 ( 107 /*) , and appear to be comparable to the trichomes of the pure species 

 Jiig/ans nigra; that is, there appears in this case to be a nigra reversion. 

 The short secreting trichomes were most numerous, so that accordingly 

 the measurements on them were most complete. Both of the hybrids 

 from which the disk-shaped trichomes just reported on were taken were 

 examined as regards the short secreting trichomes. On the trichomes the 

 following series of measurements were taken: (l) length of entire organ, 

 (2) length, and (3) diameter of the head. The relative age of the leaf 

 and the position occupied on it are both recorded in table 20. 



TABLK 20. Measurements on short secreting trichomes, hybrid No. /.* 



*In this and subsequent tables (v) refers to the location on a vein; where the 

 letter is not given the trichome is understood to be placed between the veins. 



The averages of these measurements are as follows: Dorsal surface, be- 

 tween veins, entire length, 32 /*; length of head, 18 /*; diameter of head, 

 24.7 /*. Ventral surface, between veins, entire length, 24 /*; length of 

 head, 14.2; diameter of head, 20.5 ^; on veins, entire length, 28.7 /"; length 

 of head, 15.9 /*; diameter of head, 22.5 /*. 



The leaves of both series of hybrids were not entirely mature; they were 

 in each instance 84 /* in thickness. 



