PURE SPECIES AND HYBRIDS OP JUGLANS. 



27 



It takes its origin as a slender papillate projection of the epidermis, which 

 is early cut off by a transverse wall, and which may occasionally be laid 

 down somewhat above the general level of the epidermis. From a 

 comparison with this type of trichome in other species it is probable 

 that after the young - trichome is separated from the epidermis it under- 

 g'oes one additional transverse division when the distal cell enlarges 

 and becomes the head and the proximal cell the stalk. Longitudinal walls 

 are laid down in the terminal cell in such fashion as to cause the organ- 

 ization of 4 similar and radially placed cells. With this the cell formation 

 in the region of the head is completed. 



The stalk forms two other transverse walls (but it was not surely de- 

 termined whether the fourth stalk-cell was formed during or after the 

 divisions in the head as given above) when the cell-divisions in the region 

 of the stalk are completed. The trichome thus is composed of 8 cells, 4 of 

 which constitute the head and 4 the stalk. This relation was fairly con- 

 stant, and may have held in all cases, since when the number of stalk-cells 

 was more than 4 the head was relatively large and may always have had 

 more than 4 cells. 



Table 9 gives the measurements on long secreting trichomes of the type 

 just described. 



Table 9. Measurements on long secreting trichomes of Juglans nigra. 



The heads of the trichomes average 17.6 /* in length and 37.4 n in diam- 

 eter. The variation from the average length is 12.5 per cent, and the 

 variation from the average diameter is 14 per cent. From these measure- 

 ments it is seen that the heads of the long trichomes of the 4-celled type 

 are considerably shorter than the analogous ones in Juglans calif arnica and 

 that the relation of length to diameter of the head in the two species is 

 also unlike; the diameter is the greater in Juglans nigra and the length is 

 the greater in Juglans calif or nica . But the variation from the average length 

 is identical in the two species, and the variation from the average diameter 

 is nearly the same. 



The long secreting trichome of the second type, that with more than 4 

 cells constituting the head, is fairly abundant in Juglans nigra. This type 

 of trichome has a stalk of from 5 to 9 cells and a head of about 8 cells 

 Only a few stages in the development of the trichome were seen, but these 



