THE FRUIT AND THE SEED 281 
Perisperm. In the ovule the embryo sac is surrounded by 
the nucellus. Just as the embryo absorbs food material from the 
endosperm, so the endosperm absorbs food material from the nu- 
cellus. In most seeds the nucellus is entirely absorbed before the 
seed is ripe, and even the inner integument may be so absorbed. 
In some cases, however, the ripe seed contains an embryo sur- 
rounded by the endosperm, and this, in turn, by the nucellus. 
When the nucellus remains in the mature seed it is known as 
perisperm. 
Seed coats. The seed coats are derived from the integuments 
of the ovule. The outer seed coat, or testa, develops from the 

Fic. 270. Lima bean, showing ventral, dorsal, and lateral views and embryo 
At left: m, micropyle; h, hilum. At right: embryo with seed coat and one 
cotyledon removed ; r, radicle ; p, plumule; c, cotyledon. (x 1) 
outer integument. The testa is usually thick and hard (ig. 268). 
The inner seed coat, or tegmen, is usually thin (Fig. 268). This 
is derived from the inner integument. In some cases there 1s 
only one seed coat. | 
Hilum. On the testa there is a scar marking the place where 
the funiculus was attached to the ovule (Fig. 270). This scar 
is known as the hilum. 
Micropyle. The testa is pierced by a small hole, the micropyle 
(Fig. 270), which is the same structure as the micropyle in the 
ovule. The tip of the radicle points toward the micropyle. 
