———-- 
98 The Botanical Gazette. [Marc 
verticillaris and probably R. repens, R. bulbosus and R. fae 
cicularis, though in the last three species the roots at he 
very tip show to a certain degree a blending of tissues, al 
perhaps the plerome and periblem could be said to coalest 
with the dermocalyptrogen and so belong to Erickson’s thitt 
type. He certainly says R. repens belongs there, but aly 
sections would indicate that the plerome and periblem wert 
distinct in origin though slightly confused by later gro h 
The roots of two plants examined differed from the is 
type only in that the epidermis can be traced as a disti 
layer entirely about the periblem, whiie in the first type tt 
epidermis ended as a distinct layer before the vegetatil 
point was reached. In this, as in the first type, the root-cip 
is derived from the epidermis, for though the epidermis @ 
be traced entirely around the vegetative point, it gives ® 
layers of cells which are distinctly a part of the root-ti) 
This variation from the first type is so slight as to warrant & 
at most in simply establishing a subsidiary type. The st® 
ture for this subsidiary type is shown for Ranunculus Ps fr 
sylvanicus in plate IV, fig. 31. The epidermis is distin® 
traced both by its peculiar appearance and by being 4! 
tinuous, unbroken layer entirely about the tip of the com 
the origin of root-cap cells from this layer is indicated 
and 6 of the figure; the cortex is of several rows of 
which are reduced to two at the tip and do not coalesce 
either the epidermis on one side or the central cylinder 
the other. Thus we find a distinct plerome, p/ a 
blem, #, and a combined dermocalyptrogen, @. ite 
from the first type only in that the epidermis does not 7 
its identity, though giving birth to the root-cap by 
division on its exterior side. The only other plant I certé 
place in this provisional type is R. acris. Other spec! 
doubt referred to the first type may possibly belong t? 
subsidiary type. . : 
2. My second main type corresponds to Ericksom 
type in which all the tissues merge into one at the ves®™ 
point, that is, the initial group is a common one for all 
sues. As an example of this type I have taken the root 
of Aconitum Noveboracense.2 In this root the eple® 
seen to be of cells which are larger than the other cells of 
root tip, and can be traced from above the root CaP, 
*Plate rv, figs. 32, 33. 
