LEAVITT : TRICHOMES OF ROOT. 
287 
differentiating division was observed to have taken place, in a cer¬ 
tain row, in the 12th cell from the growing point, under the root- 
cap (pi. 16, fig. 16). The cell was tabular, half as long as high 
(radially). A straight transverse dividing wall had been laid down 
separating the original cell into two almost equal parts, representing 
the first stages of the atrichomic and trichomic components of the 
epidermis. That the two segments are often nearly equal was ascer¬ 
tained. As a rule, however, the basal or proximal segment is the 
shorter. In general, the division wall is curved toward the root 
apex as it approaches the exterior. Not infrequently its position is 
somewhat oblique, and the resulting segments are therefore some¬ 
what wedge-shaped. 
The proximal segment is the more highly refractive in appearance, 
and a short time after its formation its contents become dark and 
granular. As a rule it elongates little with the growth of the tissue. 
This cell is the trichoblast. The distal cell of the pair very soon 
becomes turgid and convex, pressing in upon its sister cell, and in 
contrast to the latter, rapidly elongates, ultimately attaining to many 
times its original length. The epidermis thus consists of two kinds 
of cells, not remarkably unlike at the moment of their derivation 
from common mother cells, but exhibiting, even before they have 
escaped from under the short root-cap, a strong contrast in size, form, 
and contents. 
At a little distance back of the root-cap, the trichoblasts develop 
into trichomes. The incipient hair, as a papilla in which the nucleus 
often lies, at first turns towards the root apex (pi. 16, fig. 17). The 
base of the mature trichome is often much compressed between the 
convex ends of the adjacent elongated cells, but spreads out where 
it abuts upon the subjacent cortical layer, as well as externally, at 
the foot of the tube (pi. 16, figs. 17, 18). 
The trichoblast commonly does not divide longitudinally, although 
instances of such division may be found. The hairs are therefore 
borne singly, as a rule. When the trichome is viewed in tangential 
section it is seen that the hair emerges somewhat laterally. The 
hair occupies the position that one of the two hairs would hold, 
had the trichoblast divided longitudinally for the production of a 
pair of trichomes. This peculiarity is interesting, for it is found in 
other species of Lycopodium when the trichoblast remains undivided. 
The lateral position of the hair upon the trichome base is charac- 
