HILUM. 57 



CHAPTEE IX. 



THE FRUIT. 

 2. OF THE SEED. 



117. THE seed is the ultimate product of vegetation, and con- 

 tains the rudiments of a new plant, similar in all respects to the 

 original. 



a. The seed consists of three principal parts; the INTEGU- 

 MENTS, the ALBUMEN, and the EMBRYO. 



118. The INTEGUMENTS, or coverings, invest the seed immedi- 

 ately exterior to all its other parts. Although apparently single, 

 they consist of several membranes, to each of which an appro- 

 priate name has been applied. The first, or outer membrane, 

 is the TESTA; the second, the MESOSPERM; the third, the ENDO- 

 PLEURA, corresponding with the primine, &c. (90) of the ovule. 



a. The testa is either papery (membranous), leathery (coriaceous), horny (crus- 

 taceous), bony, fleshy, or woody. Its surface is generally smooth, sometimes 

 beautifully polished, as in the Indian shot (Canna), or columbine, and often 

 highly colored, as in varieties of the bean, &c. It is sometimes expanded into 

 wings, as in the Arabis, and sometimes into a tuft of hairs at one end, called 

 coma, as in the silk-weed, or it is entirely enveloped in hairs, as in the cotton. 



6. The coma must not be confounded with the pappus (99, a), which is a modi- 

 fication of the calyx, appended to the pericarp, and not to the seed, as in the 

 achenia of the thistle, dandelion, and other Composite. 



119. The aril is an expansion, proceeding from the summit of 

 the funiculus, or seed-stalk (91), (or from the placenta when 

 the funiculus is wanting) either partially or wholly investing 

 the seed. A fine example is seen in that gashed covering 

 of the nutmeg, called mace. In the celastrus it completely 

 envelops the seed. In other seeds it is a mere scale, and often 

 it is wanting. 



120. The HILUM, or scar, is that point or mark left on the coats 

 of the seed, by its separation from the funiculus (stalk). It is 

 commonly called the eye, as in the bean, pea, maize, &c. (Fig. 

 11; 8, a.) 



121. The hilum of the seed sometimes corresponds with the chalaza of the 



