252 GENERAL BOTANY 



The small triangular swelling on the seed of the 

 Bean, at one end of its hilum, represents an aril in 

 a very rudimentary state. It is sometimes called the 

 strophiole (p. 49). 



3. As the ovule develops there is formed in it 

 a hollow space, really a gigantic cell called the embryo 

 sac, which gradually increases in size till it occupies 

 the whole seed, the nucellus being literally consumed by 

 it. Only in a few cases, e.g. in NYMPH.EA the Water 

 lily, ARGEMONE the yellow Mexican Poppy, and PIPER 

 the Pepper, does this not happen. In these, some of 

 the nucellus remains in the ripe seed (comprises in- 

 deed most of it) and then is called perisperm. 



Inside this embryo sac there develops the embryo, 

 but before it matures the space is filled with a 

 translucent soft substance, which from its likeness 

 to moderately boiled white of egg has been named 

 albumen. We must not, however, confuse it with 

 real albumen which is a very different substance. 



In some species the albumen gradually becomes 

 dense and hard as the seed ripens, so that the ripe 

 seed contains only it and the embryo which lies in 

 it or round it. It is then called endosperm and such 

 seeds are termed albuminous or endospermous. The 

 Castor-seed is a familiar example of this. 



In other cases the albumen disappears, being literally 

 consumed by the growing embryo (just as the nucellus 

 was by the embryo sac) which eventually comes to 

 fill the whole embryo sac, and hence the whole of 

 the seed. This is the case with the Melon, Bean, Pea 

 and Gram. Such seeds are termed exendospermous, 

 or more simply, as seeds without endosperm. 



