ON THE SEED. 



237 



from two Greek words, sperma, signifying seed, and der- 

 ma, skin. 



The spermoderm, like the pericarp, is composed of 

 three coats. 



Emily. Derived, no doubt, from the two surfaces, and 

 the pabulum of the leaf, of which it is formed. 



Mrs. B. Precisely. The external skin, called Testa, 

 or cuticle, corresponds with the epicarp ; the cellular 

 coating, denominated Mesosperm, with the mesocarp ; 

 and the internal skin, called Endopleura, represents the 

 endocarp. 



When this leaf first shoots, it is hollow, and contains a 

 nutritive juice called Jimnios : the germ attached to its ax- 

 illa, when fructified, begins to absorb this fluid : it takes 

 the name of embryo ; and is, in fact, a plant in minia- 

 ture. In proportion as the amnios diminishes, the em- 

 bryo fills out and occupies the vacant space : in the course 

 of time it grows so large as to distend the spermoderm 

 itself. Here is a very young bean : I slit open the sper- 

 moderm, and you see the embryo plant surrounded by the 

 amnios. 



Emily. But it is the miniature of a bean, not that of 

 a plant. 



Mrs. B. It is the cotyledons of the embryo plant which 

 form the greatest part of this little bean : the radicle and 

 plumula are enclosed within them, and are not sufficient- 

 ly developed to be distinguished without the aid of a mi- 

 croscope. But here is a full grown bean, in which the 

 embryo occupies the whole interior of the spermoderm, 

 the amnios having been all absorbed. Now, if you sepa- 

 rate the cotyledons, you will perceive the skeleton of the 

 plant lodged between them, and making a slight inden- 

 ture in either cotyledon. 



Caroline. I see it perfectly ; but it is not in the centre 

 of the bean. 



Mrs. B. No ; it is situated at that end by which the 

 bean was connected with the pod by a short pedicel. 

 This spot is commonly called the eye or hilum of the seed. 



1292. From what Greek words is the term Spermoderm derived? 

 1293. Of how many coats is it composed'? 1294. What are they 

 called and to what do they correspond! 1295. What is the Amniosl 

 1296. Whence originates the embryo, in what proportion does it increase, 

 and what is said of it as seen in a young bean 1 1297. By the aid of a 

 microscope in the young bean! 1298. What further appears in the 

 ftill grown bean 1 ? 1299. What is the eye of the seed, and what con- 

 veys nourishment to the embryo plant! 



