ITS STRUCTURE AND PARTS. 



331 



indicated when considering the structure of the ovule. The cha- 

 laza and raphe (567), when present, are commonly obvious in the 

 mature seed, as well as in the ovule (Fig. 455, b). The terms ortho- 

 tropous, anatropous, campylot.ropous, &c., originally applied to the 

 ovules, are extended to the seeds which result from them ; so that 

 we may say, Seeds anatropous, as well as Ovules anatropous, &c. 



625. Aril (Arillus). Some seeds are furnished with a covering, 

 usually incomplete and of a fleshy texture, wholly exterior to their 

 proper integuments, arising from an expansion of the apex of the 

 seed-stalk, or funiculus, or of the placenta itself when there is no 

 manifest seed-stalk. This is called the ARIL. It forms the pulpy 

 envelope of the seed of Podophyllum, Euonymus, and Celastrus, 

 or a mere lateral scale in Turnera, or a tough, lacerated body, 

 known by the name of mace, in the Nutmeg. In the White Water- 

 Lily it is a thin, cellular bag, open at the end (Fig. 453). 



It does not appear in the ovule, but is developed subse- 

 quent to fertilization, during the growth of the seed. Of 

 the same nature is the CARUNCLE which grows from the 

 hilum in Polygala, forming a loose lateral appendage. 

 Strictly speaking, it is to be distinguished from the STRO- 

 PHIOLE, the latter being a cellular growth from the micro- 

 pyle ; but the two are not well discriminated. A similar cellular 

 growth takes place on the raphe of the Bloodroot, of the Prickly 

 Poppy, and of Dicentra, forming a conspicuous crest on the whole 

 side of the seed. 



626. The Nucleus, or kernel of the seed, consists of the ALBUMEN, 

 when this substance is present, and the EMBRYO. 



627. The Albumen (Fig. 451, d, 456,/) also variously named 



the PERISPERM or the ENDOSPERM 

 which forms the floury part of the 

 seed in our various kinds of grain, 

 consists of whatever portion of the tis- 

 sue of the ovule persists, and becomes 

 loaded with nutritive matter accumu- 

 lated in its cells, sometimes in the form of starch-grains prin- 



FIG. 453. Seed of Nymphaea (White Water-Lily), in its membranaceous sac-like aril. 



FIG. 454. Vertical section of a seed of Elodea Virginica, showing the two integuments of 

 the seed, and the embryo. 



FIG. 455. Seed of Delphinium tricorne (anatropous), enlarged : a, the hilum ; b, the raphe ; 

 c, the chalaza. 456. Vertical section of the same : c, the chalaza ; d, the testa ; e, the tegmen ; 

 f, the albumen ; g, the minute embryo near the hilum, a. 



