EFFECTS OF CLIMATE.

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In general, young plants contain a larger proportionthan old ones, and as seeds contain a supply of all thatyoung plants require, a quantity of these salts is neces-sary for the ripening of seed: hence plants require alarge supply of inorganic matter from the soil duringthe third period of their existence, or during the forma-tion of seed.

367. These are, in very general terms, the conditionsrequisite to the growth of plants ; but there are manyspecial conditions appropriate to particular species, andmany important circumstances which must not be over-looked in studying the chemistry of vegetation. The dif-ferences of climate, and its influence on the growth ofplants, is not less remarkable than those of the soil itself;and indeed the very same soil would possess a verydifferent degree of fertility in different climates.

368. In the hot, moist regions of the tropics, plantsgrow with far more rapidity, and vegetation is morevigorous, than in temperate regions. In tropical coun-tries, decay proceeds far more rapidly than it does inour own country; carbonic acid and ammonia, the foodof plants, are produced in greater quantity than here;whilst, from the greater power of the sun, plants areable to assimilate more of those substances than theycan in colder countries.

369. Hence, in endeavouring to introduce into onecountry the plants of another, it is necessary to considerthe conditions under which they naturally grow; andcare must be taken to imitate as closely as possiblethose conditions, not merely as regards soil, but likewise