44 SEED. [CHAP. 



substances which they contain being made available for the 

 use of the growing plant. The radicle is always the first to 

 break out, curving down towards the earth, whatever may 

 be its position. The radicle, by its direct prolongation, 

 forms the primary root of the plant. The plumule shortly 

 after disengages itself, ascends and developes into the stem 

 of the Pea, bearing foliage and flower-leaves. 



14. We have already briefly described the structure of 

 the seed of the Pea, which we found to consist of an embryo 

 enclosed by the testa, or seed-coat. Take now, for com- 

 parison with the seeds of the Pea, a few fresh seeds of the 

 Castor-oil plant. The hilum or scar indicating the part at 



Fig. 30. Seed of Pea ; to the left the einbn'o, with the cotyledons laid open. 



which the seed was attached in the cavity of the fruit is at 

 the top of the seed, and the micropyle, which it is difficult 

 to discover in the ripe seed, is close to it. Remove the 

 thin shell-like and prettily mottled testa, and also the thin 

 membranous inner covering of the seed, and at the top, 

 immediately under the micropyle, you may find the point of 

 the radicle of the embryo directed upwards. Cut the seed 

 through lengthwise and at right angles to its greatest breadth, 

 beginning at the radicle, and you will find its parts as repre- 

 sented in the accompanying cut (Fig. 31). An embryo, con- 



