ANATOMY OF THE CELL. Bol: 
soon changes to sugar, and when this material is not carried off 
fast enough to prevent its aggregation in the chlorophyll grain, 
it is again changed into starch. This process is known as CO, 
assimilation, as it begins with the separation of CO, and H,O 
into their elements, which are afterward reunited into carbo- 
hydrates. In the Florideae and other algae with different 
colored pigments the chlorophyll exists but is concealed by the 
other coloring matter. 
Chromoplastids include all color grains except the chloro- 
plastids. In the higher plants they are not confined to the 
flower leaves but occur in various parts. Very few have been 
found in the lower plants ; in vascular cryptogams they occur 
only in the fertile stem of Hquisetum arvense, and in mosses, in 
the antheridium wall. In form they vary from small, nearly 
spherical, to long, rod-shaped bodies. While they furnish the 
coloring matter of plants to some extent, in most cases the color 
pigment is not connected with any structure but is dissolved in 
the cell sap. 
Leucoplastids are small colorless structures whose function 
is still a disputed question. They were first discovered in 1854, 
but little notice was taken of them until Schimper took up the 
subject in 1880. They are very easily dissolved, and for this 
reason were so long overlooked. ‘They are found in nearly all 
cormophytes but rarely in thallophytes. They occur in stems 
which contain reserve material, in tubers, and in growing parts 
of plants where cells are dividing, also in epidermal cells. They 
vary in form from nearly spherical to flat, lens-shaped bodies. 
It has been proved that the starch grain originates in the chloro- 
plastids, also that after it changes into a soluble carbohydrate it 
again appears in cells not containing chlorophyll. In these cells 
not only are leucoplastids present, but they are often found with 
starch grains in various stages of development imbedded in them 
or adhering to their surface. From these facts some have drawn 
- the conclusion that the office of the leucoplastid is that of a 
