132 FOOD OF PLANTS. 



171. Nitrogen has generally been considered ar, performing 

 an unimportant part in vegetation, entering into the compo- 

 sition of some vegetables, but not into all. Boussingault in a 

 memoir published in the tenth volume of the '' Annales des 

 sciences naturelles" proves that nitrogen is a .constant and 

 necessary element of perfect vegetation. That in cases where 

 vegetables were made to grow by excluding it from the roots 

 only, the seeds were not perfected. In an experiment on 1586 

 grains of Trefoil seeds containing when the experiment com- 

 menced .114 of a grain of nitrogen, the agency of nitrogen 

 is abundantly established. These were made to germinate 

 and gro.v in silicious sand, previously heated to redness, 

 to destroy all organic substances, and watered with distilled 

 water, and at the end of three months the nitrogen had increas- 

 ed to 156 of a grain, thus gaining from the atmosphere .042 

 of a grain of nitrogen ; thus proving beyond a doubt that ni. 

 trogen is taken into the plant as a part of its food. These 

 experiments were performed with the utmost precaution, that 

 nothing but pure atmospheric air should have access to the 

 plants. Different experiments were continued during differ- 

 ent times, and the accession of nitrogen was in proportion to 

 the length of the time the expriment continued, under similar 

 circumstances. 



172. From various considerations, Boussingault comes to 

 the conclusion that nitrogen forms an important part in vege- 

 tation. It is admitted, he says that the force of vegetation is 

 in proportion to the nourishing saps, which are met with in 

 the earth, understanding by nourishing saps, those parts of 

 manure capable of being absorbed by the spongiole of the 

 root; that, in a word, which constitutes the fertility of the 

 soil, 'i haer has shown, that those manures procure for lands 

 the greatest fertility, which contain the greatest proportion 

 of animal matter, and he (15.) has shown, that those are most 

 nutritive, which contain the greatest quantity of nitrogen, and 

 that those plants empoverish the soil most, which contain 

 the most nitrogen. Hence concluding that the exhaustion of 

 the soil is occasioned by the abstraction of azotic matter, 

 which makes a part of the nourishing saps, and that, to re- 

 store to the soil the degree of fertility, which it possessed be- 

 fore cultivation, it is necessary to introduce by manure an 

 equivalent quantity of this same azotic matter. Some crops, 

 he says, (and it is well known) increase the fertility of soils, 

 such as grasses, which are cut while green, since the greatest 

 amount of nitrogen is required in perfecting the seed, and in 

 this case this exhaustion is saved ; now, the roots remaining 



