TIIK FOOD OF VEGETABLES. 



119 



success, as it contained no earthy matter wliat- 

 ever, and as the seeds grew in it, and sent out 

 ) their roots perfectly well when it was properly 

 ] moistened with water. The oxides of antimony 

 and zinc were the substances which answered 

 best alter sulphur. The seeds, then, were planted 

 in sulphur, placed in a garden at a distance from 

 all dust, put into a box to which the light and 

 air had fi'ee access; but from which all dust and 

 rain were carefully excluded, and they were 

 watered with distilled water. The com raised 

 in this manner, was found by Schrader to con- 

 tain more earthy matter than had existed in the 

 seeds from which it had grown. Here then, it 

 would appear, was the formation of earthy mat- 

 ter, unless we conceive that tlie air might have 

 contained a sufficient quantity floating in it, to 

 furnish all that was found. Subsequently Schra- 

 der has given to the public additional experi- 

 ments on the same subject. In these, he notices 

 the trials of Saussure, and the results which were 

 obtained from vegetables growing in calcareous 

 and granitic soils, and particularly draws the 

 attention of chemists to the fact ascertained by 

 Saussure, that plants vegetating in a calcareous 

 soil, which contained little or no silica, were 

 yet found to yield a considerable portion of that 

 earth. Einhof likewise found in the ashes of 

 the common fir, which had grown in a soil 

 that yielded no traces of lime, no less than 65 

 per cent of that earth. 



If the eai'ths, then, that are contained in vege- 

 tables, are derived chiefly from the soil, in 

 what peculiar state of combination do they enter 

 the vessels of the plant ? The state most likely to 

 facilitate their absorption, is that of their solu- 

 tion in water, in which all the earths hitherto 

 found in plants are known to be in a slight de- 

 .gree soluble. 



Lime is soluble in water with the aid of a 

 little carbonic acid, in the proportion of about 

 f J-jf part of its weight; but it is also soluble even 

 without the aid of the acid, and the solution is 

 known by the name of lime-water. Clay is 

 soluble in water by means of the mineral acids ; 

 and also, though very sparingly, in pure water, 

 from which even the filtre cannot abstract it. 

 .Silica is soluble in water by means of carbonate 

 of potash, as is evident from Black's analysis of 

 the waters of Geyser in Iceland. It is soluble 

 also in pure water, according to the analysis of 

 Klaproth; and in that state of division in which 

 it is precipitated from its solution in fixed 

 alkalies, it is perfectly soluble in 1000 parts of 

 water. Magnesia is soluble in water by means 

 of the mineral acids, and even in pure water, in 

 very small quantities ; requiring about 2000 times 

 its weight to hold it in solution. 



All the earths, then, found in plants, are less 

 or more soluble in water. And if it be said 

 that the proportion in which they are soluble is 



so verj' small, that it scarcely deserves to bo 

 taken into the account, it is to be recollected 

 that the quantity of water absorbed by the 

 plant is great, while that of the earth necessary 

 to its health is but little, so that it may easily 

 be acquired in the progress of vegetation. 



Such is the manner in which their absoi-ption 

 seems practicable : but the following experiments 

 afford a presumption that they are actually ab- 

 sorbed by the root. Woodward took three 

 plants of spearmint, one of which he made to 

 vegetate in distilled or pure water; another in 

 river water; and a third in water mixed with 

 mould. At the commencement of the experi- 

 ment the first plant weighed 114 gi-ains; at the 

 end of the experiment it weighed 155 grains, 

 being augmented by 41 grains. The water ex- 

 pended was 8863 grains, and the increase as 

 1.214 -f-. At the commencement of the experi- 

 ment, the second plant weighed 28 grains, at 

 the end 54 gi-ains, being augmented by 26 

 grains. The water expended was 2493 grains, 

 and the increase as 1 : 95 -f-. At the com- 

 mencement of the experiment the third plant 

 weighed 92 grains, at the end 876 grains, being 

 augmented by 284 grains. The water expended 

 was 14950 grains, and the increase as 1 : 62 -}-. 



From the greater proportional augmentation 

 of the plant to which the mould had access, we 

 may infer the beneficial effect of the eai'ths as 

 applied to the root, and perhaps the absorption 

 of a part ; particularly as it is known that the 

 proportion of earths contained in the ashes of 

 vegetables, depends upon the nature of the soil 

 in which they grow. The ashes of leaves of the 

 rhododendron ferrugineum, growing on Mount 

 Jura, a calcareous mount, yielded 43.25 pai'ts of 

 earthy carbonate, and only 0.75 of silica. But 

 the ashes of leaves of the same plant, growing 

 on Jlount Brevin, a granitic mountain, yielded 

 two parts of silica, and only 16.75 of eai-thy 

 carbonate. 



It is probable, however, that plants are not 

 indebted merely to the soil for the earthy parti- 

 cles which they may contain. They may ac- 

 quire them partly from the atmosphere. Margray 

 has shown that rain water contains silica, in the 

 proportion of a grain to a pound; which, if it 

 should not reach the root, may possibly be ab- 

 sorbed along with the water that adheres to the 

 leaves. 



But although the earths are thus to be re- 

 garded as constituting a small proportion of 

 vegetable food, they are not of themselves suffi- 

 cient to support the plant, even with the assis- 

 tance of water. Giobert mixed together lime, 

 alumine, silica, and magnesia, in such propor- 

 tions as are generally to be met with in fertile 

 soils, and moistened them with water. Several 

 dirt'erent grains were then sown in this artificial 

 soil, which germinated indeed, but did not thrive; 



