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A TEXTBOOK OF THEORETICAL BOTANY 



Starch grains in endosperm are of the large storage type which is 

 characteristic also of underground storage organs of the vegetative plant, 

 though they are seldom as large. They may be rounded, or polygonal from 

 mutual pressure when they are closely packed. As in other storage tissues 



Fig. 1369. — Phytelephas macrocarpa. Fruit in 

 cross-section, showing the hard white 

 endosperm which is used as " vegetable 

 ivory". 



the grains show concentric lamellation around a growth-centre or hilutn, 

 which may be central or excentric in the grain. Tightly packed grains may 

 occupy the whole cell, to the almost complete exclusion of cytoplasm and 

 nucleus, and they then give the endosperm a hard or bony consistency, as in 

 the " flint " grains of Zea mais, while in " mealy " endosperms they are 

 relatively isolated and rounded. The fine structure of starch grains will 

 be dealt with under Physiology in Volume III. 



Fatty oils may be present in the cells in the form of minute droplets, 

 often to a large amount. Among the richest in oils are the various " nuts". 

 For example, Pinus koraiensis (the Korean Pine), Canarium (Pili nuts) and 

 Carya pecan all contain over 70 per cent, of oil on a dry-weight basis, and 

 Walnut, Macadamia nuts, Brazil nuts and Coconut all have over 65 per 

 cent. Most of the typically oily seeds are below these percentages, e.g., 

 Linseed, 36 per cent.; Groundnuts, 47 per cent.. Sunflower, 41 per cent., 

 Cottonseed, 33 per cent. Seeds which are characteristically starchy have 

 often very low percentages of fats; ^.o.. Wheat and Barley about 2 per cent. ; 

 Peas and Broad Beans, less than 1-5 per cent. 



The term protein, as applied to reserves, covers also amides and free 

 amino-acids, the former, especially asparagin, being often present in con- 

 siderable amounts. Native proteins and amides may accompany starch in 

 the cells, generally in granular form, or they may occupy a special layer 

 of cells, normally on the periphery of the endosperm, as in the Wheat 

 grain, known as the " aleurone layer", which is free from starch. Proteins 



