HYBRIDS OF JUGLANS. 



55 



are uniformly larger than those of hybrid No. 1, which is a larger plant. 

 The form of the heads is, with one exception, the same in both series of 

 plants . 



It has been noted, in the tables and the averages, that the heads of the 

 trichomes are wider than long, and this also is a character that distinguishes 

 nigra from calif ornica . The relative form of the heads of the short secret- 

 ing trichomes in the pure species and the form of the head in this, the 

 second-generation plant No. 4, are shown in the figures. Therefore it 

 appears that we here meet a well-defined instance of reversion to the pure 

 species nigra. 



JUGLANS CALIFORNICA X JUGLANS REGIA, SECOND GENERATION. 



Measurements were made on trichomes taken from the leaves of plants 

 A and C, which were among the largest and smallest, respectively, of those 

 of this generation. The study was carried out mainly on the short secret- 

 ing trichomes, for the reason that this type was most numerous, although 

 some measurements also were made on the disk-shaped trichomes. The 

 long secreting trichomes in the material examined were not present in 

 numbers large enough to make a satisfactory study of them. 



TABLE 22. Measurements on short secreting trichomes, hybrid No. A . 



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

 veins 32.94 p, length of head 18.5 /*, diameter of head 30.4 /*; on veins, 

 entire length 40.2 /*, length of head 21.7 /*, diameter of head 32.1 /*; 

 ventral surface, between veins, entire length 27.04 p-, length of head 

 14.4 /*, diameter of head 27.8 /*; on veins, entire length 28.67 /*, length 

 of head 15.25 p, diameter of head 27.75 /*. 



