LEAVITT: TRICHOMES OF ROOT. 
291 
atrichoraic elements, and have not escaped observation. The degree 
to which they characterize the group has apparently not been under¬ 
stood, however, and their origin has not been determined by the 
observers who have described the hair-cells as being peculiar. The 
notes of several investigators, quoted below, represent practically the 
entire literature of the subject, as far as Monocotyledons are 
concerned. Species named without comment have been determined 
by me to possess the characteristic trichomes of the group. But, 
before the investigated species are enumerated, two typical cases 
may be described with some particularity. 
JLimnocharis emarginata (pi. 17, fig. 31-33).— If a freshly 
growing root be sectioned longitudinally, the fundaments of the 
trichomes may be seen, let us say, within twenty cells of the apex. 
In a particular section examined, the 18th and 19th cells in a certain 
row were tabular in form, with a radial height exceeding twice their 
individual lengths. The 20th cell had lengthened and become nearly 
isodiametric. The nucleus, in the last phases of division, was lying 
near the proximal end of the cell, preparation having thus been 
made for the cutting off of a short proximal segment, the trichoblast 
(pi. 17, fig. 31, T). From this point backward, a succession of alter¬ 
nating denser and less dense, shorter and longer cells could be 
followed. The trichoblasts at first are tabular. A short distance 
back of the edge of the root-cap, the atrichomic cells, which were 
not often divided, had become very greatly elongated, the trichomic 
cells relatively very little elongated (pi. 17, figs. 31, 32). The base 
of the matured trichome is longest where it meets the underlying 
cortex, and narrows to the foot of the hair (pi. 17, fig. 33). Base 
and hair are well supplied with protoplasm. The nucleus, which is 
not extraordinary in size but stains more deeply than the nuclei of the 
atrichomic cells, lies in the base of the trichome, or less frequently a 
short distance up in the tube. 
Sagittaria Eatoni (pi. 17, figs. 43, 44).— The origin of the tricho¬ 
blasts may be studied in the finer rootlets without sectioning. 
Before differentiation the young epidermal cells, near the apex of 
the root, become nearly isodiametric. In each mother cell a seg¬ 
ment occupying from one fourth to one third of the space at the 
proximal end is cut off by a straight transverse wall (pi. 17, figs. 43, 
44). In tangential section the trichoblastic segment may be slightly 
lenticular. The subsequent development of this cell resembles that 
