PLANT TISSUES 127 
of two or more rows of superimposed cells). The head varies 
from a one- to many-celled structure. The drug Lupulin consists 
of the glandular hairs separated from the strobiles of the ioe 
(Humulus lupulus). 
ScALEs are flat outgrowths of the epidermis composed of 
one or several layers of cells. They occur attached to the stipes 
of Aspidium, Osmunda and other ferns, where they are called 
“chaff scales.””» They are also found on a number of higher 
plants. 
Functions or Harrs.—Plant hairs are adapted to many dif- 
ferent purposes. They may absorb nourishment in the form of 
moisture and mineral matter in solution, e.g., root hairs. Those 
which serve as a protection to the plant may be barbed and 
silicified, rendering them unfit for animal food, or, as in the 
nettle, charged with an irritating fluid, penetrating the skin 
when touched, injecting the poison into the wound. A dense 
covering of hairs also prevents the ravages of insects and the 
clogging of the stomata by an accumulation of dust. They fill 
an important office in the dispersion of seeds and fruits, as with 
their aid such seeds as those of the milkweed and Apocynum 
are readily scattered by the wind. 
The reproductive organs of many Cryptogams are modified 
hairs, as the sporangia of Ferns. 
ENDODERMIS 
ENDODERMIS is the layer of cells, constituting the innermost 
layer of the cortex. It forms a cylindrical sheath around the 
stele in roots and stems of pteridophytes and spermatophytes. 
It also occurs around the vascular bundles of leaves. In 
Angiospermous stems it usually resembles the other parenchyma 
layers of cortex as to structural characteristics, save that it 
frequently contains more starch. In fern stems, roots of Mono- 
cotyledons and of Dicotyledons of primary growth, however, its 
cells are clearly distinguished from the other cells of the primary 
cortex by their vertically elongated form and cutinized or sub- 
erized (occasionally lignified) radial and end walls. 
_ The most outstanding characteristics of typical endodermal 
cells are to. be found in their walls. These may be thin or thick 
