. A textbook of botany for colleges and universities ... Botany. REPRODUCTION AND DISPERSAL 915. the gluten layer, is filled with small aleurone grains (fig. 1211); in most other seeds the aleurone grains are scattered among the starch grains or the drops of fat. Some- times, as in Ricinus (fig. 1210), the protein grains are large and contain inclusions, such as pro- tein crystals and globoids, the latter composed in part of calcium-magnesium phosphate. Protein crystals also may lie free in the cell sap, as in the cortex of the potato tuber (fig. 1206); such crystals differ from inorganic crys
. A textbook of botany for colleges and universities ... Botany. REPRODUCTION AND DISPERSAL 915. the gluten layer, is filled with small aleurone grains (fig. 1211); in most other seeds the aleurone grains are scattered among the starch grains or the drops of fat. Some- times, as in Ricinus (fig. 1210), the protein grains are large and contain inclusions, such as pro- tein crystals and globoids, the latter composed in part of calcium-magnesium phosphate. Protein crystals also may lie free in the cell sap, as in the cortex of the potato tuber (fig. 1206); such crystals differ from inorganic crystals in being able to take stains and to swell in certain media. In the algae, nitrogenous foods occur in the pyrenoids (fig. 106). The distribution of foods in seeds and the associated advan- tages. — In nearly all seeds there occur nitrogenous and non-nitrogenous foods, the lat- ter always dominating in amount. Commonly Qne form of non-nitrog- enous food dominates in any given case, so that one may speak of starchy, oily, or horny seeds. The percentage of carbon in fat is about 77 per cent, as compared with 44 per cent in starch, yet because of its greater density, a given volume of starch contains about as much carbon as does the same volume of fat. The chief advantage of fatty seeds would seem to be that their relative lightness facilitates dispersal, while on the other hand starchy seeds are better fitted for quick germination, since the amount of oxygen required to make starch available for growth is much less than that for fat. Thus it is distinctly advantageous that large seeds generally are starchy; where they are not starchy, germination is very slow (as in the coconut). Among the seeds that are slow to germinate are those with " reserve cellulose," as in the date. The influence of external factors upon the formation of accumulating foods. —- Moderately high temperatures are favorable for seed maturation and also for maxi- mum starch production, the opti
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