24 A TEXTBOOK OF GENERAL BOTANY 
Plastids. These are definitely shaped protein bodies embedded | 
in the cytoplasm. There are several kinds of plastids, and they 
have different functions. Chloroplastids are green bodies which 
are colored by chlorophyll. In the presence of sunlight, carbon 
dioxide and water are changed into sugar in the chloroplastids. 
Amyloplastids are white plastids in which starch is stored. 
Chromoplastids are variously colored plastids which in some 
cases are responsible for 
the color of flowers, fruits, 
and other organs. 
The units of living mat- 
ter. The cell is the small- 
est unit of living matter 
capable of continued inde- 
pendent life and growth, 
but examination of a cell 
has shown that it is com- 
posed of a number of dif- 
ferent smaller units, all 
of which combine to carry 
on the varied activities of 
the cell. In later chapters 
of a nipa palm (Nipa fruticans), showing W® shall have occasion to 
protoplasmic connections between adjacent Study the structure of the 
cells small units which we have 
‘The white areas represent thick cell walls observed in the cell, and 
we shall find that some of 
them are in turn very complex and composed of different kinds 
of smaller units. While the cell is, therefore, the smallest unit 
of living matter capable of continued independent existence, 
it is itself a very complex structure composed of many varied 
smaller units. 
In at least many cases the cells of higher plants are not abso- 
lutely independent, as the protoplasm of neighboring cells is 
connected by means of fine protoplasmic strands which run 
through perforations in the cell walls. When the walls are thin 

Fig. 14. Cells from the kernel of a fruit 
