146 BRITISH PLANTS 
cereal seeds are starchy ; rhizomes, bulbs, and tubers 
possess large stores of starch. In a few cases the reserve 
is sugar: the fleshy root of the beet is loaded with it ; 
the onion is sugary; so are some seeds. In other seeds 
oil is a form of reserve—e.g., nuts—and in a few cases the 
reserve is even stored up as cellulose in the cell-walls, 
which then become enormously thickened—e.g., the date- 
stone. Nitrogenous food-reserves are found chiefly in 
seeds, but they are seldom so important as carbohydrates, 
and rarely give rise to conspicuous swollen structures. 
The Seats of Storage of Food-Reserves. 
In what follows, food-reserves in plants are only dealt 
with in so far as these stores are serviceable to man, either 
as a source of food, or on account of their value for 
economic purposes. 
1. The Seed.—The food- 
material stored up in seeds 
is for the use of the young 
plant during its germina- 
tion, and during that 
period of infancy known 
as the seedling-stage, when 
Fie. 52.— LoneirupinaL SECTION jt jig unable adequately to 
or ALBUMINOUS SEED OF ONION. : 
(MaanrerEp.) supply its own needs. In 
a, seed-coat ; b, endosperm ; c, embryo. albuminous seeds (Figs. 52, 
53, 54) this reserve of food 
lies outside the embryo in the cells of the endosperm— 
e.g., wheat, iris, spindle-tree, poppies, buttercups, and all 
the Umbellifere. In exalbuminous seeds (Fig. 55) the 
food is stored in the embryo itself, usually in the coty- 
ledons, which are then large—e.g., pea, bean, acorn, sun- 
flower—but sometimes in the hypocotyl—e.g., brazil-nut, 
which is, botanically, not a nut at all, but a’seed with 
a hard shelly coat. 
(a) Carbohydrate reserves occur in the form of— 
(i.) Starch, in starchy seeds—e.g., the cereal grains, 
wheat, barley, rice, etc., which yield flour when ground. 
(ii.) Sugar in sugary seeds—e.g., certain varieties of 
maize. 
(6) Protein occurs in the form of amorphous particles 
(aleurone grains) or crystals, which may be either dis- 
