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CHAPTER XI.
THE PROCESS OF VEGETATION. USE OF THE COTYLEDONS.
When a seed is committed to the ground it swells by the moisture which its vessels soon absorb, and which, in conjunction with some degree of heat, stimulates its vital principle. Atmospherical air is also necessary to incipient vegetation, for seeds in general will not grow under water, except those of aquatic plants, nor under an exhausted receiver: and modern chemists have determined oxygen gas, which is always an ingredient in our atmosphere, to be absorbed by seeds in vegetation. An experiment is recorded in the Philosophical Transactions, No. 23, of sowing Lettuce-seed in two separate pots, one of which was placed iu the common air, the other in the vacuum of an air-pump. In the
