170 



HUTCHINSON'S POPULAR BOTANY 



Thus in the one case the embryo forms the entire kernel of the seed ; 

 and in the other it is surrounded by a mass of albuminous tissue or endo- 

 sperm, and occupies but a small part of the kernel. On this account, seeds 



of the latter kind are called albuminous, while 

 those which, like the bean, contain no sur- 

 rounding nutrient matter, are said to be 

 exalbuminous. The terms are somewhat mis- 

 leading, however, as the substance contained 

 in the seed is not identical in chemical com- 

 position with animal albumen. It has charac- 

 teristic differences in various plants. Thus it 

 is mealy or farinaceous in cereals ; fleshy in 

 the Barberry (Berber-is) and Heartsease (Viola) ; 

 oily in the Poppy (Papaver) and Coconut 

 (Cocos nucifera) ; mucilaginous in the Mallow 

 (Malva) cartilaginous in the berry of the 

 Coffee-plant (Coffea) ; and hard and white like 

 ivory in the Negro's Head Palm (Phytelepkas 

 macrocarpa). The endosperm of this palm 

 forms the " vegetable ivory " of commerce. 



In some seeds a part of the albuminous 

 substance owes its origin to layers of cells 

 outside and different from those which produce 

 the endosperm, and hence it is given the dis- 

 tinguishing name of perisperm. In seeds of the 

 Water-lily family (Nympha&aceaz), for example, 

 the embryo plant is embedded in endosperm, 

 which occupies the narrow end of the seed, 

 while the rest of the albumen consists of 

 perisperm. Ripe seeds of the Cannas (Can- 



. naceoe), again, have no endosperm at all, 



the whole of the nutrient substance being 

 perisperm. 



For important reasons of classification the 



number and position of the cotyledons of seeds 



should always be carefully noted. AYe have 

 seen that tn e spores of Fungi, Mosses, Ferns, 

 and other cryptogamic plants never have 

 cotyledons- they are not true seeds. We 

 have also seen that grains of Barley and 



Maize, though possessing those organs, provide but one with each 

 embryo ; while both the Bean and Mustard seed have two. Therefore, 

 looked at with reference to the germinating body, the plants above 

 enumerated are of three kinds : those entirely destitute of cotyledons, 



FIG. 210. A GRAIN OF BARLEY 

 BEFORE GERMINATION, AND THE 



