NUTRITION 
389 
food accumulates. This may be the parenchyma of the cortex, or of 
the vascular bundles, or of the pith; or all may be involved. One note- 
worthy point is that the storage tissues are composed of live cells, even 
though, as in some ferns, they are very thick-walled. It is to be observed 
also that the reservoirs of food are usually located in parts that persist 
through a dry or cold season unfavorable to growth, and that have rudi- 
mentary growing points capable of quick and vigorous development 
by using the adjacent surplus. So the seeds, 
bulbs, tubers, rhizomes, etc., are organs of 
propagation, and by way of attaining that end 
become also organs of storage. (See Part III 
on seeds, bulbs, and tubers.) 
Storage cells active. The storage of food 
is not merely a stuffing of passive cells with 
surplus food; it involves the activity of the 
storage cells themselves, at least for the ac- 
cumulation of the food, and usually also for 
the mobilization when this food is about to 
travel to growing regions where it is subse- 
quently used. The process of mobilization is 
commonly called digestion (see p. 397), and 
seems to be the reverse of the process by onia: 660, simple starch grain 
which the storage forms of food are pro- th , kucoplast in position; 
66i,leucoplast alone of a simi- 
duced. 
Storage forms. The storage forms of food 
are chiefly starches, sugars, hemi-celluloses, 
inulin, fats, and proteins. From this list it will be apparent that carbo- 
hydrates predominate, and quantitatively they form much the greater 
part of stored food. 
Starches. Starches are stored in the form of grains, many having a 
form characteristic of the plant in which they are found. The grains are 
organized by the activity of cell organs called leucoplasts or amyloplasts 
(figs. 660-662), which seem to take the material as it comes to the cells, 
perhaps as glucose, and combine it into larger and more complex mole- 
cules, that finally become starch. This is disposed in the interior of the 
leucoplast as one or more grains, which at length stretch it enormously, 
or even rupture it. The actual structure of the grain is believed to be 
that of a spherite; that is, it is composed of a multitude of microscopi- 
cally minute, threadlike crystals, radiating from its organic center. If 
lar grain; 662, leucoplast of 
a twin grain, x 900. After 
MEYER. 
