PURE SPECIES AND HYBRIDS OF JUGLANS. 



29 



48.3, 50.4, 50.4, 56.6, 46.2, 52.6. That this is a type of trichome distinct 

 from the 4-celled one is apparent from the diameters of the head. The 

 smallest head of the 8-celled type is considerably larger than the largest of 

 the 4-celled form, while the largest is more than 25 per cent larger than these . 



No study was made of the excretions or especially of the structure of 

 the secreting cells; the 8-celled type was the only one which gave indica- 

 tion of marked activity in this regard. In such trichomes as shown in fig. 

 7, c, it appears as if the secretion is held for a time between the layers of 

 the cell -walls which are on the distal end of the trichome. The appear- 

 ance figured was not observed in other trichomes. 



The short secreting trichomes occur on both surfaces of the leaf; they 

 measure from 27.3 /«■ to 50.4 ^ in length. Whatever may be the size of the 

 trichome the terminal group of cells is relatively short, so that the head 

 has a squat appearance. 



The early stages in the development of the short secreting trichome are 

 apparently similar to those of the same type of trichome in Juglans cali- 

 fornica. As usual for the trichomes, the origin is to be traced to rather 

 narrow outgrowths of epidermal cells. The young trichome undergoes 

 two successive transverse divisions, by which it is separated from the epi- 

 dermis and by which the initial of the head is differentiated from that of the 

 stalk. The following division is probably longitudinal in the head-cell, 

 followed by a division of the stalk, by which the divisions in the stalk are 

 concluded, and this is followed by the second and third longitudinal divisions 

 of the head, which take place in such manner that 4 radially placed cells 

 result. With the organization of a head of 4 cells and a stalk of 2 cells 

 the cell-division in the trichome ceases. 



Table Vi.— Measurements on short secreting trichomes from young leaves, 



Juglans nigra. 



