HISTOLOGY OF VEGETABLES. 
5 
the primary elements discoverable in both these grand 
divisions of the organic world. 
The vegetable kingdom is divided by the philosophical 
botanist into two great classes, the cellulares and the 
vasculares ; the former containing the lowest, and there- 
fore the least complicated forms. In this class the fungi , 
algce and lichens , are composed of simple cells alone, 
occasionally elongated or otherwise modified in shape in 
the higher types of each order. The lowest form in each 
of these orders is a simple globular or ovoid cell. As 
we proceed, two or more cells are united in a definite 
form. Still further development occurs in higher 
groups until we find distinct organs, which, in the 
highest of the algce and lichens bear a striking simili- 
tude to the leaves and seed-vessels of the vascular or 
flowering plants. Some orders of algos , the Desmideoe 
and Diatomaceas for example, are equally claimed by the 
botanist and the zoologist, so uncertain is it to which 
department of science they truly belong. 
In the vascular class of plants, the structure is more 
complex, the organs are numerous and serve distinct 
purposes, and their elementary tissues have been 
divided into cells, fibres, and vessels : this subdivision 
has been proved by recent investigation to be illusory ; 
vessels being merely modified or elongated cells ; and 
fibres, elongated cells, the walls of which are thickened, 
or the entire cavity solidified by subsequent deposit on 
the internal surface of the cell wall. 
The lowest types of animal life consist, like the analo- 
