Dr. Hugo Mohl, on Liebig's Organic Chemistry. 97 



in the beginning of growth, the number of twigs, sprouts, or leaves 

 overpass this proportion in consequence of a superabundance of food 

 obtained from the soil at that period, when the plant requires more 

 food from the air for the completion of its development, and for its 

 flowering and fruiting than the air can supply it with, blooming and 

 fruiting will not take place. In many cases, such food will merely 

 suffice for the development of leaves, stems, or branches. 



Here Dr. Mohl complains of the strange ambiguity of this part of 

 Liebig's theory. In one instance (says M.), the usual quantity of 

 humus in the soil suffices merely to form leaves, and if we want an 

 abundant harvest, we must get it by conveying a maximum of 

 food from the soil. On the other hand, humus adds nothing to the 

 crops, but, on the contrary, is noxious, by conveying too much food, 

 for it causes the production of too much foliage, a sufficient supply 

 of food for which cannot be obtained from the air. Whence, 

 then, does it arrive that a plant which has many leaves can not ob- 

 tain from the air the food required for blooming, although it can do 

 so if it has only a few leaves ? It has been hitherto supposed that 

 the reception of food from the air was in proportion to the number 

 and size of its leaves ; and this is plausible, but the contrary is not. 

 When a plant standing in a moist and shaded situation grows too 

 luxuriantly, and will not flower, the reason is not to be sought in a 

 deficiency of food, but rather in its superabundance, and its influence 

 on the too luxuriant development of its vegetative organs ; for 

 that will counteract the contraction of the axis and the metamor- 

 phosis of vegetative into floral organs. 



Another statement, however, shows how Liebig arrived at the 

 above conclusion. He says that, after the completion of its leaves, a 

 plant does not require more carbonic acid from the soil ; and 

 that even perfect dryness of the soil will not impede the completion 

 of its growth, if the plant continues to receive from dew and 

 air the amount of moisture required for the process of assimilation-, 

 and that, in fine, it will derive in a hot summer its whole carbon ex- 

 clusively from the atmosphere. 



This assumption (says Dr. Mohl) is the result of an erroneous 

 view of the fact, that in many plants — by no means in all — such or- 

 ganic substances are employed for the development of fruit, as, hav- 



