GROUP IV. — PHANEROGAMIA. 459 



sperm 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 extra-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. 112), and are present in all seeds. The non-nitro- 

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

 p. 109), in starchy seeds (e.g. Peas, Beans, Cereals, etc.) ; or fat, 

 in the form of oil-drops (see p. Ill), 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. Euphorbiaceae, Rosaceoe) : 

 in others again neither of the ovular integuments persists into the 

 seed, in which case the wall of the embryo-sac is in direct con- 

 tact with the wall of the ovary. 



In a few cases additional integuments or appendages are de- 

 veloped in connexion with the seed, such new growths being 

 designated by the general term aril. The aril may be developed 

 from either the funicle or the hilum ; or from the micropyle, when 

 it is distinguished as an arillode. Good examples of a funicular 

 aril, which grows up round the seed like an additional integument, 

 are afforded by the Yew, Water-Lily (Nymphaea), Passion-Flower. 

 The Willow has a funicular aril in the form of a tuft of woolly 

 hairs. The most striking example of a membranous micropylar 

 aril is the Spindle-tree (Euonymus) : in Euphorbia and Polygala 

 the micropylar aril is a small mass of tissue, and in Asclepias it 

 is a tuft of hairs. Other excrescences, not especially connected 

 with either the hilum or the micropyle (sometimes distinguished 



