354 Proceedings of the 



the soil under the plough; these plants, in their decomposition, 

 return to the soil the carbon which they had borrowed from it, and 

 also enrich it with that which they had derived from the atmosphere. 

 It may appear paradoxical, but it is unquestionably true, that some 

 soils furnish too much aliment to plants : thus wheat growing in a 

 very rich soil, will have an exuberance of leaves, and the stems, borne 

 down by their own weight, are bent towards the earth, by which the 

 vegetation is suspended and no grain is produced. Even the stems 

 which remain in an upright position produce very little grain ; the 

 superabundance of nutrition, producing in the plant the same effect 

 as obesity in animals, considerably diminishes its generative power. 

 The cause of this phenomenon must be sought in an examination of 

 the mechanism of vegetable nutrition. 



The alimentary carbon derived from the soil is converted into 

 carbonic acid by the oxygen of the atmosphere, which the plant 

 absorbs by means of its respiration ; this carbonic acid is then de- 

 prived of its oxygen by the influence of the light, and it is then that 

 the alimentary carbon, being set at liberty, assimilates itself with the 

 plant which it nourishes. It follows, therefore, that if the extractive 

 matter obtained from the soil be so great, that it cannot all be mo- 

 dified by the oxygen of the air, and assimilated by the light as above- 

 mentioned, the plant will be gorged with juices imperfectly prepared, 

 which will be incapable of performing the most important act of 

 organization, that of sexual generation. The nearer the stems are 

 to each other, the more this effect on the leaves will be perceptible, 

 since they mutually keep the light from each other, and the influence 

 of light being indispensably necessary to the elaboration of the nutri- 

 tive juices, many of the leaves, particularly the lower ones, become 

 blanched and die. Count Chaptal, in his l Chimie applique'e a 

 1* Agriculture,' has noticed this phenomenon, and has also remarked, 

 that when, by excess of manure, a soil has been raised to an exuberant 

 state of nutrition, the produce will taste of the manure, which proves 

 that the alimentary carbon has not been properly elaborated or pre- 

 pared : thus the quality and flavour of grapes grown on a vine which 

 has been abundantly manured, will be found far inferior to those 

 grown on a vine which has been carefully and moderately manured. 

 We often hear agriculturists remark, that fields of wheat, which have 

 appeared luxuriant and flourishing in the spring, have belied their 

 promise, and afforded but indifferent harvests ; the cause of this is 

 now evident to the physiologist, the plants had derived too abundant 

 a nutrition, and their functions, instead of being properly developed, 

 were smothered and rendered inert. Hence, it is of the greatest im- 

 portance, for practical agriculturists to study well the character of the 

 soil with which they have to do, that they may avoid giving it too 

 much, as well as too little artificial nutrition. It is well known to 

 horticulturists, that trees which exhibit a great luxuriance of boughs 

 and leaves, rarely, if ever, produce fruits or flowers ; this is also a 

 result of a superabundance of nutrition, but is produced in a different 



