176 PLANT ANATOMY. 
v7. The system of receptacles for secretions. ~ Function: to re- 
ceive the products of secretion of the plant.’ 
1. The Epidermal System. 
While such plants and parts of plants which consist of a single 
cell, or of but a single layer, do not possess an epidermis,’ a 
more or less distinct development of epidermal layers appears 
already in the thallophytes and cormophytes, which have the 
thickness of but a few layers of cells. The cells in these layers 
become for the most part smaller and more thick-walled toward 
the exterior, and often colored, even though the formation of a 
true epidermis is not yet effected (Secale cornutum, Fucus vesicu- 
losus, Cetraria, Usnea, Spherococcus, the small stems of 
mosses). : 
It is only in the higher plants that, even in the youngest 
stages, a true epidermis is formed, and this is the first of any 
system of tissue which is sharply defined, morphologically, from 
all the others. 
It consists in most cases of a row of tabular or plate-like cells, 
laterally united without intervening spaces, which in the organs 
of dicotyledons are, as a rule, of quadratic form, in the elon- 
gated leaves and stems of monocotyledons, however, are mostly 
extended in the direction of the axis of the organ (distinct upon 
surface sections). On many roots the epidermis is also sharply 
defined from the other tissue by a different color and strongly 
sinuous outer walls. Such an epidermis, which we meet with, 
for example, on the rootlets of Helleborus niger and Veratrum 
' Sachs classifies the tissues as follows: epidermal tissue, fascicular 
tissue, and fundamental tissue. In the above division we adhere to the 
classification of Haberlandt (‘* Physiologische Pflanzenanatomie,” Leip- 
zig, 1884), which is based upon Schwendener's principles. Nevertheless 
the expression ‘‘ fundamental tissue ” (filling tissue) may often be permit- 
ted in the following pages on account of its brevity, notwithstanding 
the fact that the fundamental tissue comprises the most varied forms 
of tissue. 
2’ End upon, and éépue skin, 
