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 disting'uishes 

 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 /*, length of head 18.5 z^, 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 /*, length of head 

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

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



