244 ANATOMY AND PHYSIOLOGY OF PLANTS. 



32. The interior integument lines the testa and im- 

 mediately envelopes the nucleus. Like the outer coat, 

 it consists only of one piece, of a soft and pulpy texture 

 till the embryo has reached maturity, at which period it 

 becomes membranaceous, and may generally be sepa- 

 rated with ease from the nucleus. 



It is said to derive its origin from the interior portion of the um- 

 bilical cord, which after perforating the outer coat, disperses into a 

 multiplicity of ramifications connected by a fine membrane. 



33. On the outer surface of the interior covering, is 

 found in many, but not in all seeds, a small deep-coloured 

 areola, or a small spongy or callous tubercle, called the 

 chalaza or internal scar. 



It is placed near the external scar, or diametrically opposite, as it 

 frequently occurs that the nmbillical cord, after penetrating the testa, 

 passes on without ramifications to the opposite side of the cavity, 

 and there forms the chalaza, as in the case of the cherry. 



34. The nucleus is that part of the seed which is 

 contained within the proper integuments, consisting of 

 the albumen, the vitellus, the cotyledon, the radicle and 

 the plumelet. 



35. The albumen is that portion of the seed which 

 invests the cotyledons, resembling both in consistence 

 and colour, in many seeds, the white of a boiled egg. 



Although the albumen is wanting in some seeds, it most be ad- 

 mitted, when present, to be a substance of considerable importance. 

 It supports and defends the embryo, whilst this essential part is im- 

 prisoned in the seed, and serves for the nutriment of the embryo, 

 when it begins to germinate. 



