Dr. Hugo Mohl, on Liebig s Organic Chemistry. 83 



respective branches. Now this sort of nutrition from substances 

 derived from living plants is also proper to a very large number of 

 parasites (Loranthacae) which are quite green, and therefore provided 

 with organs for decomposing carbonic acid. Such plants are entirely 

 similar in structure to those which grow in soil ; but they must, of 

 necessity, possess the capacity of feeding on substances already assi- 

 milated by other plants. To these true parasites are to be added 

 the spurious parasites, which feed on decaying organic matter, 

 amongst which some have green leaves, and others are destitute of 

 that colour. The latter can have no capacity for decomposing car- 

 bonic acid, forming organic matter from it and water. The same is 

 also the case with many other plants of a green colour, which al- 

 though they decompose carbonic acid, still are proved by their place 

 of abode to be dependent for their food on organic matter in a state 

 of decomposition. From this series of plants there is but a step 

 toward those growing in peat and heath- soil, &c. I do not mean, 

 concludes Dr. Mohl, to prove by these statements that all plants 

 feed on organic substances ; my object is rather to explain that the 

 introduction of organic matter into the system of vegetation is not, as 

 Liebig asserts, necessarily detrimental to the economy of plants; 

 and to show that it is by far preferable to have recourse to positive 

 and precise experiments, than to indulge in groundless and general 

 remarks and theories. 



In the second chapter {Origin and Nature of Humus,) Liebig 

 states, that vegetable matter is successively changed by decomposi- 

 tion into humus, and that it constantly forms a carbonic acid with the 

 oxygen of the atmospheric air ; all which forms a constant source of 

 nourishment for plants, which decompose both the carbonic acid 

 taken up by the roots, and that obtained by the leaves from the air. 

 This, says Dr. Mohl, was known long ago. New, however, most 

 certainly, is the argumentation by which L. intends to prove (p. 56) 

 that humus is unnecesssary, and that plants derive their food ex- 

 clusively from the atmosphere. In corroboration thereof, he adduces 

 the antediluvian and tropical vegetation, and says of the former, that 

 its gigantic Plams, Graminese (sic !), and Ferns, could dispense alto- 

 gether with soil, on account of the immense development of their 

 foliage, as they are also distinguished from those of the present 



