DESCRIPTION OF PLATES. 175 
Puant Hairs. (Puate TX. Fie. 2.) 
The surface of the leaves of certain plants 
presents a glistening appearance (e. g., ice-plant), 
due to the presence of little elevated transparent 
vescicles which appear like drops of dew at- 
tached to the leaves. Under a low magnifying 
power it will be seen that these are simply cells 
of the epidermis which are elevated above the 
general level to form little hemispherical pro- 
jections, which, being filled with fluid and having 
a transparent cell-wall, glisten like dewdrops. 
Again, instead of a hemispherical projection, 
we may have a little cone, as in the cabbage leaf. 
This is a plant hair, and in its simplest form it is 
nothing more than an elongated cell of the epi- 
dermis. But nature does not confine herself to 
simple and stereotyped forms, seeming rather to 
delight in variety and even eccentricity in the 
moulding of the cellular elements out of which 
plants and animals are built. Thus these plant 
hairs may be composed of a single cell having a 
spherical (calyx of Salvia) or bulbous extremity ; 
or of a cell enormously elongated ; or of a cell di- 
vided at its extremity into two or more branches 
(Draba, Allysum). Again, they may be composed 
of a linear series of elongated or spherical cells (sta- 
mens of Tradescantia). The typical cell is spheri- 
cal, and we can easily account, under mechanical 
laws, for changes in form resulting from pressure, 
as in the pith of plants, etc. But what is the 
