CHAPTER I THE MATERIAL INCOME OF PLANTS 
I. THE PLANT CELL 
An organ. At a glance one sees that the body of an ordinary green 
plant, such as a bean, is segmented, certain parts being clearly marked 
off by form from others. The colorless root grows in the soil; the green 
shoot grows in the air and consists of a distinct stem with lateral out- 
growths, the leaves. Anatomically, these parts 
are members; but as the work of the plant is 
distributed among them, each has its functions, 
and physiologically each is an organ. 
A cell. When one of the organs of the bean, 
such as a leaf, is inspected, one sees that it, 
too, is made up of parts, the petiole and the 
leaflets. The latter are composed of ribs and 
veins, with green tissue, or mesophyll, between. 
These parts also have certain functions and 
hence may be called organs. A microscopic 
examination of the mesophyll reveals that it is 
composed of minute bits of material which has 
come to be known as living, and is called pro- 
toplasm. Each, individualized, is a protoplast, 
separated more or less completely from its neigh- F 
bors by membranes which it and they have a mesophyll cell of a leaf; 
formed. The membrane and protoplast con- c ' chloropiast; , nucleus; 
v, vacuole ; w, cell wall, 
stitute a cell (fig. 619). 
Organs of a cell. When the protoplast is examined more closely, 
a general translucent material, the cytoplasm, may be distinguished from 
various inclusions. There are (a) many very minute particles, whose 
nature is obscure, which tend to make the cytoplasm opaque; (6) minute 
clear spaces, more fluid and sometimes watery, the vacuoles, many 
of which coalesce as they enlarge with age, and form a few relatively 
very large water spaces or only one; (c) a roundish nucleus; (d) numer- 
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