On Superphosphate of Lime. 



233 



as require no preparation by combination with the materials of 

 the soil, but are at once, and in the form in which they are 

 applied, taken up by the plant and appropriated to its nourish- 

 ment. The former of these assumptions is in a manner dependent 

 on the latter, for, if plants can really take up and make use of the 

 different substances furnished to them in manure in the state in 

 which we apply them, there seems no good reason why thev 

 should wish for more. But I confess that the unexpected aspect 

 which has been given to the question of the food of plants by the 

 experiments made by Mr. Thompson and myself would lead to 

 a far different conclusion. The impression left on my mind by 

 these experiments, unsatisfactory and incomplete as they still are^ 

 is that the ofhce of the soil, not merely as a place for the roots of 

 plants to take root in and obtain a mechanical attachment to, but 

 as an agent for the alteration and preparation of these manures — 

 itself taking part in the necessary changes — is of the very last im- 

 portance to healthy vegetation. Of this circumstance there is no 

 doubt — that healthy vegetation of land plants will not proceed in 

 water whatever may be the care and attention given to supplying 

 the plants with food, whilst the same food distributed through a 

 given quantity of soil becomes at once available to the sustenance 

 of plants. It is also certain, from the experiments alluded to, 

 that the ingredients of manure, both mineral and organic, do enter 

 into a new state of combination with the soil, and that conse- 

 quently, in the ordinary course of nature, plants do directly take 

 these means of support and growth from the compounds so formed. 

 It needs therefore only a very small amount of logical reasoning 

 to convince us that, as this is the usual and natural, so it must be 

 the healthiest and best form in which the substances which con- 

 stitute the food of plants can be offered to their acceptance. 

 Sulphate and muriate of ammonia, added to water in which the 

 roots of plants are placed, not only fail to nourish but actually 

 destroy them. On the other hand, these salts distributed through 

 a small portion of soil produce the most luxuriant vegetation. 

 If again we find that sulphate of ammonia, and the muriate of 

 the same base, immediately after mixture with the soil cease to 

 remain as such, but enter into union with certain ingredients of 

 the soil J are we not justified in believing that it is this new com- 

 bination, or something derived from it, which is effectively the 

 food of the plant, and that the soil is an all-powerful agent in the 

 preparation of that food ? 



I am unwilling to form a conclusion of this importance without 

 due and careful consideration, but it does appear, to say the least, 

 questionable whether plants can healtliily subsist on the crude 

 and various substances supplied in manure until these substances 



