GERMINATION OF THE SEED. 



137 



Fig. 90 



Fig. 90 represents a young mono- 

 cotyledonous plant ; at a is the cotyle- 

 don ; at b is the second leaf, which, in 

 the example just given of the rye, ap- 

 peared on the sixth day ; at c is the 

 primordial leaf, which at first envelopes 

 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 

 through which the extremities have 

 forced their way.f It has been ob- 

 served, that moisture is essential to the 

 germination of the seed. Earth, 

 though not absolutely essential, is use- 

 ful, as affording to the vegetable egg 

 a favourable situation, where it may 

 receive the influence of the various 

 agents, which are to perform their offi- 

 ces in the developement 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 nourishment. 

 It is however sufficiently apparent that 

 plants may vegetate without earth. 

 The parasite grows upon the bark of 

 other plants ; many seeds vegetate in 

 water, and some, if moistened and 

 placed on cotton, or other supporting 

 substance. 



Air is essential to vegetation ; un- 

 der an exhausted receiver a seed will 

 not germinate, although possessing 

 every other requisite. Seeds that be- 

 come imbedded deeply in the ground, 

 do not vegetate, unless accidentally 

 ploughed up, or exposed to the contact 

 of the atmosphere. Acorns which are 

 supposed to have lain for centuries, 

 have germinated as soon as they were 

 raised sufficiently near the surface to 

 receive the influence of air. 



* This, the French botanists call the pileole. 

 t This covering, Mirbel terras the coleorhize. 



Explanation of Fig. SO Earth useful to vegetation Air essential to vegetation. 



12* 



