ORGAN IC AtAlTKltS OP Til K SOIU S35 



(we use this word ns a general collective term) to rain- 

 water, and tlie richer the soil, as made so by manures and 

 judged of by its productiveness, the larger ihe quantity, 

 up to certain limits, of humus it contains. If, as we have 

 seen, plants always contain silica, though this element be 

 not essential to their development (II. C. G., p. 186), is it 

 probable that they are able to reject humus so constantly 

 presented to them under such a variety of forms? 



Liebig opposes the view that humus contributes directly 

 to the nouiishment of plants because it and its compounds 

 are insoluble; in the same book, however, {Die Chemle 

 in Hirer Anwendung auf Agricultur und Physiol ogie^ 

 7th Ed., 18G2) he teaclies the doctrine that all the food 

 of the agricultural plant exists in the soil in an insoluble 

 form. This old objection, still m.iintained, tallies poorly 

 with his new doctrine. The old objection, furthermore, is 

 baseless, for the humates are as soluble as phosphates, 

 which are gathered by every plant and from all soils. 



It has been the habit of Liehig and his adherents to 

 teach that the plant is nourished exclusively by the last 

 l^roducts of the destruction of organic matter, viz., by car- 

 bonic acid, ammonia, nitric acid, and water, togetlier with 

 the ingredients of ashes. While no one denies or doubts 

 that these substances chiefly nourish agricultural plants, 

 no one can deny that other bodies may and do take part 

 in the process. It is well established that various organic 

 substances of animal origin, viz., urea, uric acid, and gly- 

 cocoll, are absorbed by, and nourish, agricultural plants ; 

 while it is universally known that the principal food of 

 multitudes of the lower orders of plants, the fungi, includ- 

 ing yeast, mould, rust, brand, mushrooms, are fed entirely, 

 so far as regards their carbon, on organic matters. Thus, 

 yeast lives upon sugar, the vinegar plant on acetic acid, 

 tlie Peronospora infestans on the juices of the potato, 

 etc. There are many parasitic plants of a higher order 

 common in our forests whose roots are fastened upon and 



