PURE SPECIES AND HYBRIDS OF JUGLANS. 



33 



second form of long secreting trichome, which was found in/uglans nigra 

 especially, was not surely determined for this species; if, indeed, it occurs 

 in. Jtiglans regia at all it is rare. 



The short secreting trichome is to be found on both surfaces of the 

 leaves, both old and young, although it is more abundant on the latter. 

 Only two of the young stages in development of the short trichome were 

 observed. After separation from the epidermis the next succeeding cell- 

 division cuts of the head-cell from the stalk-cell. When mature the tri- 

 chome consists of 2 stalk-cells and 4 head-cells (shown in fig. 8, n\.ow). 



The short secreting trichome shows a considerable variation in size which 

 appears to be directly associated with the position occupied by it. The 

 variation is especially noticeable in the length of the head. Table 12 

 illustrates the range of variation in length of head in young and old leaves 

 and in stem. 



Table 12. — Measurements of short secreting trichomes, 

 Juglans regia. — Length of head. 



The average length of the trichomes from the dorsal surface is 29.2 /*, 

 from the ventral surface, 25.2 /^. The length of the heads of dorsally 

 placed trichomes is also slightly longer than those of the ventrally placed 

 ones; those of the former average 14.3 /* and those of the latter is 13.6 /* 

 (table 13). 



Table Ki. — Measurements on short secreting trichomes, Juglans regia. 



