THE AXGIOSPERMAE 1489 



treatment designed to soften the hard outer testa. It follows from these 

 facts that the materials stored in the soft nutritive layer of the testa cannot 

 be absorbed bv the embryo and that they are therefore consumed by the 

 outer tissues during the period of their differentiation. It is evidence of 

 the importance of the inner cuticle that it is well developed in the seeds of 

 water plants, whose vegetative organs may have little cuticular covering or 

 none. 



That some degree of mechanical protection is afforded by the testa is 

 obvious from its structure, but it is often less than might be supposed. 

 Great hardness of the testa may be compensated by lack of elasticity, so 

 that the shell is easily broken. Even the hardest seeds may be broken up 

 and digested bv ruminant animals or in the crops of some birds and when 

 the seed is softened and about to germinate the protection is least, just 

 when the need for it might be supposed greatest. Moreover, seeds collected 

 from the soil usually show more or less damage to the testa and some seeds 

 germinate so rapidly in the soil that their testas never harden at all. Seeds 

 such as those of many alpine plants must germinate thus, for they have no 

 power of longevity and protection is scarcely required. On the other hand 

 there does not seem to be any obvious correlation between great longevity 

 and a particular testa structure. 



The most extensive investigation of the anatomy of seeds is due to 

 Martin (1946). He developed a classification based on the internal mor- 

 phology of the seeds of 1,274 genera, representing two-thirds of the families. 

 The criteria used were the relative sizes of embryo and storage tissues, the 

 position of the embryo and its shape. There are five major divisions with 

 twelve subdivisions, the latter depending chiefly on the form of the 

 embryo (Fig. 1362). 



The five major divisions are as follows: 



1. Basal. Embryos relatively small and basal, in seeds that are usually 



medium to large but sometimes small. Examples: Magnoliaceae, 

 Ranunculaceae, Papaveraceae, Nymphaeaceae, Juncaceae. 



2. Peripheral. Embryos vary from small (in some Grasses and Sedges) 



to large or completely filling the seed, always contiguous to the 

 testa, at least in part, and often curved. Endosperm starchy, 

 lateral or central. Examples: Gramineae, Cyperaceae, Caryo- 

 phyllaceae, Chenopodiaceae, Cactaceae, Polygonaceae. 



3. Axile. Embryos vary from small to total {i.e., completely filling the 



seed), central, straight, curved or coiled. Endosperm not starchy. 

 Examples : Umbelliferae, Solanaceae, Liliaceae, Amaryllidaceae. 



4. Reduced. Embryos usually minute, seeds small to minute, testa thin 



and delicate. Examples: Scrophulariaceae, Gentianaceae, Cam- 

 panulaceae, Ericaceae, Orchidaceae. 



5. Foliate. Embryos usually large, sometimes total, usually central, 



cotyledons expanded, seeds usually rather large. Examples: 



