294 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
Glumiflorae. 
In Juncaceae, Cyperaceae, and many Gramineae, the specialized 
character of the trichomic cells is marked. In many members of 
the Gramineae the external differentiation of the hair-cells, though 
pronounced enough to be unmistakable, is not great. In a few 
species all distinction of trichomic and atrichomic cells seems to 
have been lost. 
As illustrative of the Glumiflorae several species may be exam¬ 
ined in some detail. 
Alopecurus occidentalis .— The development of the epidermis may 
be traced in detail in rapidly growing rootlets. The cap is very 
small; the rootlets are transparent. Proceeding from the apex, and 
following a longitudinal cell row, the following sequence of elements 
was observed in a particular case. (1) Equal sided cells, as viewed 
in full face, 9 in number. These may divide transversely, or split 
longitudinally to institute new rows. (2) Cells wider in conse¬ 
quence of the growth of the root in circumference and shorter by 
reason of repeated transverse division, up to the 22d cell from the 
apex. (3) Cells in which trichoblastic segments have been formed, 
beginning with the 23d from the apex. A regular alternation of 
dissimilar cells — trichoblasts and their sister cells — now follows. 
In longisection the wall separating the sister cells of the same pair 
is inclined backward; the lower, slightly shorter and more refrac¬ 
tive cell, the trichoblast, being thus a little wedge-shaped, with its 
thinner edge inward. (4) Trichoblasts alternating with two atri¬ 
chomic cells, beginning after the 32d cell from the apex. The atri¬ 
chomic cells in this region divide transversely (pi. 18, fig. 65). (5) 
Marked elongation of all the elements including the trichoblasts, 
which though throughout distinguishable in size and contents from 
the atrichomic elements, may nearly equal the latter. The hairs 
now appear. The evolution of the piliferous layer is complete. 
Carex crinita .— The piliferous layer presents some differences 
of appearance in different roots of the same individual plant. On 
fine rootlets observed the cells were comparatively short. Even in 
these rootlets, however, the specialized nature of the trichomes and 
of the cells destined to become trichomes is evident. In a particular 
case, typical of the roots examined, the first transverse divisions pre- 
