UNORGANIZED CELL-CONTENTS. 
15 
the chloroplastid, and is known as assimilation starch. 
The latter is changed into soluble carbohydrates by the 
aid of ferments and probably other substances, and in 
this form is transported to those portions of the plant 
requiring food. In many of the cells through which 
the solution of carbohydrates passes these substances 
may be transformed back into starch through the influ- 
ence of the leucoplastids, and this product is known as 
transitory starch. The starch in the medullary rays 
and in other cells of the wood and bark of plants is of 
this character, and is distinguished by being in the 
form of rather small and nearly spherical grains. In 
rhizomes, tubers, bulbs and seeds another kind of 
starch is produced by the leucoplastid, which differs from 
transitory starch in that the grains are, as a rule, quite 
large, and possess more or less distinct characteris- 
tics for the plants in which they are found. Starch of 
this kind is spoken of as “ depot,” “ storehouse,” or, 
more frequently, as reserve starch. 
Occurrence. — Starch is found in most of the algae and 
many of the mosses, as well as in the ferns and higher 
plants. The amount of starch present in the tissues of 
plants varies. In the root of cassava as much as 70 per 
cent, has been found. This constituent also varies in 
amount according to the season of the year. Rosen- 
berg has observed that in certain perennial plants t here 
is an increase in the amount of starch during the 
winter months, whereas in other plants it decreases or 
may entirely disappear during this period. In the 
latter case, from six weeks to two months in the spring 
are required for its re-formation, and about an equal 
period is consumed in the fall for its solution. 
metabolism, and is illustrated in the formation of starch from car- 
bon dioxide and water. The latter is known as destructive meta- 
bolism, as when sugar is changed into alcohol and carbon dioxide. 
