LEAVITT: TRICHOMES OF ROOT. 
285 
4 
of nuclear division was obtained in sections. At this stage, however, 
the obliquity of the new cell wall is already determined (pi. 16, fig. 
5, d). Of the two more or less wedge-shaped elements so formed, 
the lower and slightly larger one is the hair initial or trichoblast. 
As the root reaches the limit of its development, the hair-forming 
impulse travels downward until the apical cell itself is split into 
several parts, each piliferous. 
The trichoblast never elongates much in a direction parallel to 
the length of the root. It may divide transversely once, as in rare 
instances two trichomes are found standing in succession. The tube, 
which presently begins to grow out, turns toward the root apex (pi. 
16, figs. 7, 8, 9). As the hairs lengthen they at first lie appressed 
to the root and may be seen confined by the inner cap, which is now 
pushed away from the root trunk. The whole cap structure is finally 
thrown off through the growth of the lower hairs, and the hairs 
themselves standout strongly (pi. 16, fig. 11). Their bases retain 
the wedge form of the original hair initial (pi. 16, fig. 10). 
Soon after their organization, the hair initials are to be distinguished 
from the cells with which they alternate by their contents no less 
than by configuration, since they are more richly supplied with pro¬ 
toplasm (pi. 16, fig. 6). In the younger portion of the root the 
transverse divisions of the piliferous layer are very uniform. The 
cells therefore stand in fairly regular and continuous zones. This 
arrangement is manifested by the young hairs (pi. 16, fig. 8). 
The lesser wedge-shaped cell produced simultaneously with the 
hair initial elongates and soon divides transversely (pi. 16, figs. 7, 9) 
once, twice, and often three times. The trichomes in each longitu¬ 
dinal cell row thus become separated by two, four, or eight cells. 
The intervening cells may be six, however. The number of divisions 
in neighboring rows may be different; and through the resulting 
displacements the original regularity of the hair zones is destroyed 
(pi. 16, fig. 11). 
Equisetinae. 
Equisetum arvense (pi. 16, fig. 12-15).— The trichoblast may 
be seen under the root-cap in the longisection of the root, as narrow, 
proximal segments of lately divided epidermal cells (pi. 16, fig- 12), 
the wall of division often being curved toward the apex of the root, 
