PHAXEROGAMIA. 415 



there is perisperm but no endosperm in the ripe seed, though it has 

 been ascertained in some cases that endosperm is originally 

 formed. 



A formation of endosperm takes place in nearly all seeds, even 

 exalbuminous seeds : but in these latter it is more or less dis- 

 organised and absorbed by the growing embryo, so that little or 

 none remains in the ripe seed. 



Whether the seed be albuminous or exalbuminous, it contains 

 (except in some parasitic or saprophytic plants, such as Orchids, 

 etc.) a supply of organic substances for the nutrition of the 

 embryo during its exti'a-seminal period of development. These 

 substances may be mainly stored in the cells of the cotyledons, as 

 in exalbuminous seeds ; or in the cells of the endosperm, or in 

 the cells of the perisperm, when present, as in albuminous seeds. 

 The substances are nitrogenous and non-nitrogenous. The nitro- 

 genous substances are proteids, deposited in the solid form as 

 aleuron (see p. 80), and are present in all seeds. The non-nitro- 

 genous substances are starch, in the form of starch-grains (see 

 p. 78), in starchy seeds (e.g. Peas, Beans, Cereals, etc.) ; or fat, 

 (in the form of oil-drops (see p. 80), in oily seeds (e.g. Linseed, 

 Rape, Castor-Oil seed, etc.). 



The seed is generally enclosed in a single integument, the testa, 

 derived from the outer integument of the ovule, the inner integu- 

 ment of the ovule having been absorbed ; sometimes, however, the 

 seed has two integuments derived from those of the ovule, an 

 outer testa, and an inner endopleura (e.g. Euphorbiacese, Rosacese) : 

 in others again neither of the ovular integu- 

 ments persists into the seed, in which case the 

 wall of the embryo-sac is in direct contact 

 with the wall of the ovary. 



In a few cases additional integuments or 

 appendages are developed in connexion with 

 the seed, such new growths being designated 

 by the general term aril. The aril may be 

 developed from either the f unicle or the hilum : 

 or from the micropyle, when it is distinguished 

 as an arillode. Good examples of a funicular 

 aril, which gjows up round the seed like an 

 additional integument, are afforded by the 

 Nutmeg, where it forms the Mace ; (Fig- 246), 

 the Yew, Water-Lily (Nymphsea), Passion- 



