GERMINATION OF f Ht SEfitJ 



105 



Fig. 115. 



Fig. 115 represents^ a young- monocotylo- 

 donous plant; at a, is 'the cotyledon; at b, is 

 the second leaf, which, in the example just 

 given of the rye, appeared on the sixth day; 

 at c, is the primordial leaf,* which, at first, en- 

 velops and conceals the other leaves ; at d, 

 are the several branches of the root, bearing 

 their radicles, and at their base enveloped by 

 a peculiar covering, e,t through which the ex- 

 tremities have forced their way. 



Earthy though not absolutely essential to 

 germmation, is useful, as aflfbrding to the 

 vegetable egg a favourable situation, where it 

 may receive the influence of the various 

 agents, which are to pel-form their offices in 

 the development of its parts. It seems, too, 

 not improbable that some of the constituent 

 elements of earth may be absorbed by the 

 germinating plant and converted into nour- 

 ishment. It is, however, sufficiently apparent 

 that plants may vegetate without earth. The 

 parasite grows upon the bark of other plants j 

 many seeds vegetate in water, and some will 

 grow if moistened and placed on cotton, oi* 

 any other supporting substance. 



Air, is essential to vegetation ; under an ex- 

 hausted receiver a seed will not germinate, 

 although possessing every other requisite; 

 Seeds that become imbedded deeply in the 

 giround, do not vegetate, unless accidentally 

 ploughed up, or exposed to the contact of the 

 atmosphel-e. Acorns supposed to have lain 

 for centuries, have germinated as soon as 

 raised sufficiently near the surface of the 

 earth to receive the influence of air. 



You will recollect that in the process of ger- 

 mination, oxygen gas unites with the carbon 

 of the seed, and carries it off in the form of 

 carbonic acid. Air furnishes that important 

 agent, oXygeh, which is the first moving prin- 

 ciple of vitality. 



Carbon constitutes the gf-eater part of the 

 substance of seeds ; and this principle, being 

 in its nature opposed to putrefaction, prevents 

 seeds frOm rotting, previous to their being 

 sown. Some seeds having an abundance of 

 carbon, are capable of being preserved for 

 ages ; while others, in which this element exists 

 but in a small proportion, require to be sown almost as soon as ripe ; 

 and such as are still more deficient in carbon lose their vital prin- 

 ciple before separating from the pehcarp. 



You can now understand that oxygen is important to germination 

 on account of its agency in removing the carbon which holds the 

 living principle of the seed in bondage^ 



* Callad by Mirbel) the tj^hoh. 



t The coteothize. 



Explanation of Fig. 115— Earth nnportant to vegetation— Air esseniial to vegeta- 

 tion— Oxygen an important agent— Carbon. 



