6 
HISTOLOGY OF VEGETABLES. 
gous vegetable forms, of simple cells ; but the progress 
of development in animals is much more rapid than 
in plants, producing a greater variety of external form 
and complexity of structure among groups which 
would otherwise hold a parallel position in the two 
kingdoms. 
One great distinction between the elementary tissues 
of plants and animals, which should be always kept in 
view by the student is, that while in the plant the 
cell, however modified in form, still possesses all the 
characters of a cell ; in the animal it usually under- 
goes a development into tissues, in which the cellular 
form completely disappears, and the cellular origin of 
the tissue can only be discovered by studying it in its 
embryonic condition. 
MEMBRANE. 
It is now generally considered by vegetable phy- 
siologists that, with the addition of an intercellular 
mucus or cambium, all plants are made up of a mem- 
brane existing in the form of cells or utricles, having 
as an organic basis a tough insoluble material called 
cellulose. Membrane, therefore, is regarded as the 
sole element of plants. Some years since, fibre was 
also enumerated as an element, but more recent obser- 
vation has shown that this is always subsequently 
deposited on the inner surface of membrane. 
