56 



HEREDITY AS ILLUSTRATED BY TRICHOMES. 



Following- are the diameters, in p, of disk-shaped trichomes from leaves 

 of plant A: 54.6, 67.2, 67.2, 63, 58.8, 67.2, 58.8, 67.2, 71.3, 63, 71.3, 67.2, 

 71.3, 71.3, 71.3, which average 66 p. The following dimensions, in p-, 

 were obtained of disk-shaped trichomes from C: 67.2, 71.3, 67.2, 67.2, 

 67.2, 63, 63, 67.2, 71.3, 71.3, 67.2, which average 67.5 /*. The diameters 

 of the trichomes of the larger plant A and those of the smaller plant C 

 are nearly the same. The trichome appears not to revert to either pure 

 line, but holds an intermediate position, as in the first generation. 



Dimensions of the short secreting trichome of both of the plants A and 

 C were especially noted. These included the entire length of the trichome, 

 the length, and the diameter of the head. Attempt was made to get 

 leaves which were of approximately the same age, but it happened that 

 those of A were 10 p thicker than those of C. The former was 94 p and 

 the latter 84 /* in thickness. It will be recalled that the leaves of hybrids 

 numbered 1 and 4 were also 84 p in thickness. 



The measurements show that the length of the trichomes of the dorsal 

 surface, as well as both dimensions of the heads of trichomes from this sur- 

 face, are larger than the corresponding dimensions of trichomes from the 

 opposite leaf -surf ace, and also that all of the dimensions of trichomes 

 from the veins are greater than the dimensions of trichomes from between 

 them. The fact of reversion is not clear. The diameter of the heads of 

 the hybrid trichomes is considerably greater than that of either californica 

 or regia, and the length of the head is intermediate between the lengths 

 of the heads of this trichome in the two pure species. The proportions of 

 the head of the hybrid, on the other hand, are practically the same as the 

 proportion in the pure species regia. It is to be noted that the form of the 

 head is nearly as in the first generation of this hybrid (fig. 19). 



TABLE 23. Measurements on short secreting trichomes, hybrid No. C. 



