160 



SCIENCE OF GARDENING. 



Taut II. 



when they are prematurely cut ofF. But the farinaceous substance of the cotyledons, at least in cxa!- 

 buminous seeds, is a proof that they themselves contain the nutriment. Tliey are to be regarded, thereiorc, 

 as repositories of the food destined for the support of the embryo in its germinating state. And if the 

 seed is furnished with a distinct and separate albumen, then is the albumen to be regarded as the rejw- 

 sitory of food, and the cotyledon or cotyledons as its channel of conveyance. But the food thus contain_>d 

 in the albumen or cotyledons is not yet fitted for the immediate nourishment of the embryo. Some 

 previous preparation is necessary ; some cliange must be effected in its properties. And this cliange is 

 cftfected by the intervention of chemical agency. The moisture imbibed by a seed placed in tlie earth is 

 immediately absorbed by the cotyledons or albumen, which it readily penetrates,, and on which it imme- 

 diately begins to operate a chemical change, dissolving part of their farina, or mixing with tlieir oily 

 particles, and forming a sort of emulsive juice. The consequence of this change is a slight degree of 

 fermentation, induced, perhaps, by the mixture of the starch and gluten of the cotyledons in the water 

 which they have absorbed, and indicated by the extraction of a quantity of carbonic acid gas as well as 

 by the smell and taste of the seed. This is the commencement of the process of germination, wliich 

 takes place even though no oxygene gas is present. But if no oxygene gas is present, then the process 

 stops ; which shows that the agency of oxygene gas is indispensable to germination. Accordingly, when 

 oxygene gas is present it is gradually inhaled by the seed; and the farina of the cotyledons is found to 

 have changed its savour. Sometimes it becomes acid, but generally sweet, resembling the taste of sugar ; 

 and is consequently converted into sugar or some substance analogous to it. This is a further proof that 

 a degree of fermentation has been induced; because the result is precisely the same in the prcc.ss of the 

 fermentation of barley when converted into malt, as known by the name of the saccharine fermentation ; 

 in which oxygene gas is absorbed, heat and carbonic acid evolved, and a tendency to germination indi- 

 cated by the shooting of the radicle. The effect of oxygen, therefore, in the process, is that of converting 

 the farina of the albumen or cotyledons into a mild and saccharine food, fit for the nourishment of the 

 infant plant by diminishing the proportion of its carbon, and in augmenting, by consequence, that of its 

 oxygen and hydrogen. The radicle gives the first indications of life, expanding and bursting its integu- 

 ments, and at length fixing itself in the soil : the plumelet next unfolds its parts, developing the rudi- 

 ments of leaf, branch, and trunk : ano', finally, the seminal leaves decay and drop off; and the embryo 

 has been converted into a plant, capable of abstracting immediately from the soil or atmosphere the 

 nourishment necessary to its future growth. 



Sect. II. Food of the vegetating Plant. 



725. The substances which plants abstract from the soil or atmosphere, or the food of the 

 vegetating plant, liave long occupied the phytological enquirer What then are the com- 

 ponent principles of tlie soil and atmosphere ? The investigations and discoveries of 

 modern chemists have done much to elucidate this dark and intricate subject. Soil, in 

 general, may be regarded as consisting of earths, water, vegetable moidd, decayed animal 

 substances, salts, ores, alkalies, gases, perhaps in a proportion corresponding to the order 

 in which they are now enumerated ; which is at any rate the fact w^th regard to the three 

 first, though their relative proportions are by no means uniform. The atmosphere has 

 been also found to consist of at least four species of elastic matter — nitrogen, oxygen, 

 carbonic acid gas, and vapor ; together with a multitude of minute particles detached 

 from the solid bodies occupying the surface of the eartli, and wafted upon tlie winds. 

 The two former ingredients exist in the proportion of about four to one ; carbonic acid 

 gas in the proportion of about one part in 100; and vapor in a proportion still less. 

 Such then are the component principles of the soil and atmosphere, and sources of vege- 

 table nourishment. But the whole of the ingredients of the soil and atmosphere are not 

 taken up indiscriminately by the plant and converted into vegetable food, because plants 

 do not thrive indiscriminately in all varieties of soil. . Part only of the ingredients are 

 selected, and in certain proportions ; as is evident from tlie analysis of the vegetable sub- 

 stance given in the foregoing chapter, in which it was found that carbon, hydrogen, 

 oxygen, and nitrogen, are the principal ingredients of plants ; while the other ingredients 

 contained in them occur but in very small proportions. It does not however follow, that 

 these ingredients enter the plant in an uncombined and insulated state, because they do 

 not always so exist in the soil and atmosphere ; it follows only that they are inhaled or ab- 

 sorbed by the vegetating plant under one modification or another. The plant then does 

 not select such principles as are the most abundant in the soil and atmosphere ; nor in 

 the proportions in which they exist ; nor in an unconnbined and insulated state. But 

 what are the substances actually selected ; in what state are they taken up ; and in wliat 

 proportions? In oider to give arrangement and elucidation to the subject, it shall be 

 considered under the following heads : Water, Gases, Vegetable Extracts, Salts, Earths, 

 Manures. 



726. IFater. As water is necessary to the commencement of vegetation, so also is it 

 necessary to its progress. Plants will not continue to vegetate unless their roots are 

 supplied with water ; and if they are kept long without it, the leaves will droop and 

 become flaccid, and assume a withered appearance. -Now this is evidently owing to the 

 loss of water ; for if the roots are again well supplied with water, the weight of the plant 

 is increased, and its fi-eshness restored. But many plants will grow, and thrive, and 

 effect the developement of all their parts, if the root is merely immersed in water, 

 though not fixed in the soil. Tulips, hyacinths, and a variety of plants with bulbous 

 roots, may be so reared, and are often. to be met with so vegetating ; and many plants 

 will also vegetate though wholly immersed. Most of the marine plants ai'c of this de- 

 scription. It can scarcely be doubted, therefore, that water serves for tJie purpose of a 

 vegetable aliment. But if plants cannot be made to vegetate without water ; and if 

 they will vegetate, some wlicn partly immersed without (he assistance of scnl ; and some 



