SEEDS. 15 



fering in size or shape, and so on ; l but these peculiarities 

 are generally constant and characteristic in the species, or 

 group of species, in which they occur. Whatever the 

 form and position of the embryo, the radicle points towards 

 the micropyle. 



Food materials of various kinds are stored up for the 

 use of the plantlet during germination. If the tissue con- 

 taining such reserve materials surrounds the 

 embryo, it is called the endosperm, or, using an 

 old phraseology, the seed is said to be albuminous. If, on 

 the contrary, the reserve materials are stored within the 

 embryo itself, even if they are of precisely the same 

 nature, the seed is said to be without endosperm, or exal- 

 buminous. 2 The terms are not well chosen, but have be- 

 come so fixed as to render it necessary to recognize them. 



Certain structural peculiarities are intimately connected 

 with the developmental history of seeds. They are at- 

 tached to the mother plant by a minute stalk _ 



, , Hilnm, rapne, 



through which nutritive materials are conveyed chalaza, mi- 

 during their period of growth, but from which cr Py le - 

 they break away at maturity, leaving a scar called the 

 hilum, such as is plainly seen on the common bean. From 

 the hilum, in the great majority of cases, extends a fine, 

 fibrous bundle, the raphe, like that of the castor oil seed, 

 either the entire length of the seed, or for a shorter dis- 

 tance, ending in a point, the so-called chalaza, where the 

 seed coats cohere with each other and with the parts 

 within. The raphe is simply a continuation of the stalk 

 through which food materials were carried to the develop- 

 ing seed, the chalaza being the point where the materials 



1 Cf. Lubbock, Seedlings. 



2 For the rare cases in which a distinction must be made between 

 endosperm and perisperm, see Gray, Structural Botany, p. 310. 



