224 Inquiry into the Structure of Seeds, 



the moments of incipient germination, from or through the 

 surrounding soil. Thus the bulk of the seed is increased^ 

 and its vital principle stimulated. It bursts its immediate 

 integument, or testa, and in the first place sends forth the 

 radicle, or young root, into the ground. This part being, 

 as Dr. Darwin well observes, most susceptible of the sti- 

 mulus of moisture, elongates itself in the direction in which 

 it meets with that stimulus ; and descending into the earth, 

 while it fixes the infant plant, assumes its own proper func- 

 tion of imbibing nourishment for the future support of that 

 plant. But before any supplies can be thus obtained, con- 

 siderable demands are made, even by the root itself j and 

 not only an evolution of parts, but likewise an increase of 

 bulk, takes place in the young vegetable. For this neces- 

 sary purpose a store is prepared in the albumen, a sub- 

 stance either constituting a separate body by itself, as in 

 grasses, corn, palms, he, which, from a hard, dry, and 

 tasteless mass, changes, by the action of water and oxygen, 

 into a milky or saccharine fluid ; or the same substance is 

 lodged in, or united with, the bulk of another part, next to be 

 mentioned, the cotyledori, or, as they are generally of the 

 plural number, cotyledons. As the root is the part stimu- 

 lated by moisture, the cotyledons appear to be most stimu- 

 lated by air, and they consequently raise themselves, for the 

 most part, out of the ground in order to receive it, in the 

 form of seminal leaves well known to perform, for a time, 

 the functions of real leaves, and even, by the action of 

 light, to assume their green colour. The albumen cannot 

 be said to be stimulated, or acted upon as a living body, hy 

 the air or gas, which only produces chemical changes in it; 

 and the destination of this substance being soon accom- 

 plished, it disappears by absorption. Not so the other parts 

 of the seed, one of which becomes the still descending root, 

 the other the nurse, or, if we may say so, the foster-brother 

 of the young ascending plant, which last originates from 

 the extremity of the embryo opposite to the root, but always, 

 like that, most intimately connected with the cotyledons. 

 These indeed, sooner or later, wither away ; when the ac- 

 quisition of real and more ample foliage renders them super- 

 fluous. 



