SOWING SEEDs. 35 
T'hus we often see large trees springing from crevices in apparently 
bare rocks; while not even a blade of grass will grow among the 
moving sands of a desert. 
The reasons for the second and third points of covering the seeds, 
and yet not covering them too deeply, appear more obvious; ana 
yet they also require a little explanation. The seeds are covered te 
keep them in darkness, and to retain round them a proper quantity 
of moisture ; not only to make them swell and begin to vegetate, but 
to enable the roots to perform their proper functions; since, if ex- 
posed to the air, they would become dry and withered, and lose the 
power of contracting and dilating, which is essential to enable them 
to imbibe and digest their food. Burying the seeds too deeply is 
obviously injurious in impeding the progress of the young shoot to 
the light; and in placing it in an unnatural position. When a seed 
vegetates too far below the surface, a part of the stem of the plant 
must be buried; and this part not being intended to remain under- 
ground, is not protected from the dangers it is likely to meet with 
there. It is thus peculiarly liable to be assailed by slugs and all 
kinds of insects, and to become rotten by damp, or withered by heat. 
It is also very possible to bury a seed so deeply as to prevent it from 
vegetating atall. The ground has more of both warmth and moisture 
near the surface than at a great depth, as it is warmed by the rays of 
the sun, and moistened hy the rain; but besides this, seeds will not 
vegetate, even when they are amply supplied with heat and mois- 
ture, if they are excluded from the influence of the air. Every ripe 
seed in a dry state is a concentration of carbon, which, when dis- 
solved by moisture, and its particles set in motion by heat, is in a fit 
state to combine with the oxygen in the atmosphere, and thus to 
form the carbonic acid gas which is the nourishment of the expand- 
ing plant. For this reason, seeds and newly sprung-up plants do 
not want to be supplied with manure, and air is much more 
essential to them: they have enough carbon in their cotyledons, 
or in the albumen contained in the seed, and they only want 
oxygen to combine with it, to enable them to develope their other 
leaves; and this is the reason why young plants, raised on a hot- 
bed, are always given air, or they become yellow and withered. 
Light absorbs the oxygen from plants, and occasions a deposition of 
the carbon. Thus seeds and seedlings do not require much light; 
it is indeed injurious to them, as it undoes in some degree phat the 
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