THE ANGIOSPERIVIAE 1497 



frequently occur in crystalline form, and these crystals are conspicuous in 

 some oily seeds, e.g., BerthoUetia and Ricinus, contained in the so-called 

 " aleurone grains", throughout the reserve tissues. These grains are really 

 minute vacuoles containing water-soluble globulins and including hexagonal 

 or rhombohedral crystals of the protein, together with mineral crystals, 

 either of calcium oxalate or, usually, of calcium-magnesium phosphate in 

 the form of a spherical crystal called a " globoid". The aleurone grains 

 rapidly swell and disintegrate in contact with water, the protein passing 

 into solution. 



The amount of protein present may be very considerable, and adds 

 greatly to the food value of some cultivated seeds, though seed proteins are 

 reckoned as only of second-class value in animal nutrition because they may 

 not contain the appropriate amino-acids in suitable proportions. The 

 Soya Bean comes nearest to milk and meat in the food-value of its proteins 

 and the Groundnut and Cottonseed are nearly as good. The pulses stand 

 high in order of protein content, the Garden Pea containing over 25 per 

 cent, (dry weight). Broad Beans slightly more and Runner Beans somewhat 

 less. Soya Beans contain 37 per cent., Groundnuts 30 per cent., and 

 Cottonseed 39 per cent. 



Besides the above-mentioned reserves many other substances are found 

 in seeds, which may or may not act as reserves. Sugars occur in small 

 percentages in the cereals, mainly as sucrose. Wheat and Barley contain 

 2 to 3 per cent, and Rye 6 to 7 per cent. The seed of the Sugar-maple 

 {Acer saccharum) contains 6 to 7 per cent, of sugars and over 5 per cent, 

 of other simple carbohydrates but no starch. Notable amounts of sugar 

 occur in the seeds of the Pineapple and other Bromeliaceae, up to 13 per 

 cent, of reducing sugars in some varieties. Tannins, resins, glucosides, 

 mucilages, saponins and alkaloids may also be present, sometimes in con- 

 siderable quantities. 



A curious consequence of double fertilization, which was very puzzling 

 before Navaschin's discovery, is that the endosperm may often show 

 characters associated with the male parent. This was called xenia, in 

 reference to the " foreign " influence supposedly at work. The eflFect is 

 conspicuous in the grains of Maize, where the characteristics of the grains 

 are largely due to the endosperm. The appearance of xenia depends upon 

 whether the endosperm characters of the pollen parent are dominant over 

 those in the ovule parent or not. If they are, the endosperms on the ovule 

 parent will all follow the characters of the pollen parent. If they are 

 recessive there will be no xenia efl^ect apparent. The term metaxenia has 

 been applied to a more remote eflect of the pollen parent on the testa or 

 the pericarp. Possibly this may be due to hormones diffusing from the 

 embryo. 



A peculiarity of certain families is the possession of what is known as 

 ruminate endosperm, which refers to the invasion of the endosperm by in- 

 foldings of the outer tissues penetrating deeply and partially dividing 

 up the endosperm by long, ingrowing processes. There may also be 



