GERMINATION. 1 01 



When the young root has made some progress, the 

 cotyledons are raised out of the ground hy the ascend* 

 ing stem, take a green colour and perform the function 

 of real leaves, submitting the juices to the action of 

 air arid light ; in this state they constitute what are 

 called seed-leaves. Hadish, Mustard, and Bean are ex- 

 amples. After the plume unfolds itself into the proper 

 leaves, these seed-leaves, being no longer needed, gen- 

 erally wither and decay. 



Plants which have only one cotyledon, as the grass 

 and corn tribes, and the Orchidce, do not raise it out of 

 the ground, and it of course never becomes a seed-leak 



Observation* The substance, which makes up the principal bulk 

 of the seed with one cotyledon, has been called Albumen. There 

 is, in some of those seeds, another part, which is situated in imme- 

 diate contact with the embryo, which has been called Vitelhts or 

 yolk, very conspicuous in Indian- corn. 



The presence of air is indispensable to the germi- 

 nation of seeds. They will not vegetate in an ex- 

 hausted receiver, nor when they are buried too deep in 

 the earth, but they often retain their power to vegetate 

 for an unlimited period. Earth, taken from a consid- 

 erable depth, will, when exposed to the air, soon be cov- 

 ered with young plants, especially of the Thistle or 

 Mustard kind, though no seeds have been allowed to 

 have access to it. 



The vital principle of seeds, on which depends their 

 power to vegetate, seems not to be affected by the com- 

 mon vicissitudes of heat and cold. Some seeds lose 

 their vegetative power by being kept out of the ground 

 ever so little a while after they are ripe, and, in order 

 to succeed, must sow themselves in their own way. 

 Others may be kept a long while without losing this 

 power. Some seeds, although they will vegetate after 

 being long preserved, jet they produce stinted and 

 sickly plants. 



If the process of germination has once commenced., 

 its interruption is fatal to the seed. 



