54 



HEREDITY AS ILLUSTRATED BY TRICHOMES. 



Another study on the dimensions of the trichomes of No. 4, as will ap- 

 pear directly, gave somewhat different results. The leaves were of the 

 same thickness as those reported on above. The measurements, of which 

 there were 60, may be disregarded; the results are as follows: Dorsal sur- 

 face, entire length, 31.47 P, length of head 16.5 /*, diameter of head 21.6 /*; 

 ventral surface, entire length, 29.2 /*; length of head 16.2 /*, diameter of 

 head 22.6 p. Thus the length of the trichomes from the dorsal surface is 

 about the same in both cases, but the size of the heads is in the latter 

 instance somewhat greater. The dimensions of trichomes from the ventral 

 surface of the former are nearly the same as those from between the veins 

 of those last given. In each instance the same relation of length to 

 diameter of head is almost exactly held. 



TABLE 21. Measurements on short secreting trichomes, hybrid No. 4.. 



Attached to leaf-surface in close relation to a vein. 



tThese trichomes occurred on the same vein. 



{These trichomes were on opposite sides of the leaf and very near a vein. 



The averages are as follows: Dorsal surface, entire length, between veins, 

 33.8 A*, length of head 16.44 p-, diameter of head 25 ); on veins, entire length 

 41.84 /*, length of head 18.3 /*, diameter of head 23.5 A*; ventral surface 

 between veins, entire length 31.1 p-, length of head 19 /"-, diameter of head 

 19.70 /*; on veins, entire length 35.5 /, length of head 15.16 /*, diameter 

 of head 19.26 /*. 



The leaves studied were not fully developed; they were 84 A* in thickness. 

 If we compare the average measurements of hybrids 1 and 4 we shall get 

 the following results: (l) trichomes taken on the dorsal surface, between 

 veins, are longer in plant 4 than in plant 1, and the heads also are larger, 

 but they retain similar proportions; (2) those between the veins on the 

 ventral surface of plant 4 are also longer than in 1, and the heads are 

 longer but of less diameter (californica character ?); (3) on the veins the 

 trichomes of 4 are larger than those on the veins of 1 , but the heads are 

 shorter and of less diameter, that is to say, the trichomes of hybrid No. 4 



