VEGETABLE PHYSIOLOGY 
CHAPTER I 
THE GENERAL STRUCTURE OF PLANTS 
Examination of the body of every living organism shows us 
that it is composed of different materials, which exhibit a 
great deal of variety in the ways in which they are arranged. 
These different materials fall very naturally into two classes, 
which include respectively the living substance itself, and 
various constituents of the body which have been con- 
structed by it. The relative proportions in which these two 
classes of materials exist vary very greatly in different 
organisms; in some of the simplest forms indeed we can 
discern nothing structural except the living substance itself. 
In others the materials constructed by the latter are much 
the greatest in amount. 
When we study the life history of the simplest or the 
most complex plant with which we can become acquainted, 
we find that at some time or other in 
its existence it ig found in the form of 
a minute portion of jelly-like material 
which is endowed with life. Some- 
times this piece of living substance is 
motile, and can swim freely about in 
water by means of certain thread-like 
appendages which it possesses (fig. 1). Fre. 1—Zoospone or 
Such structures occur almost exclu. 777%" * 500. 
sively among the lowest forms of plants, particularly the 
seaweeds. They are known as zoospores, or zoogonidia, 
1 
