424 PLANTS AND THE ATMOSPHERE. 



are sprinkled with pure water. The latter disappears almost entirely by evapo- 

 ration, a very small quantity only remaining behind. The plant increases in size, 

 and gains in weight since it receives nourishment from the air, and aUo because 

 it takes it from the soil. At the end of a certain period of growth, it is gathered, 

 and then measured by new chemical analysis; first as to how much carbon, oxy- 

 gen, hydrogen, and nitrogen it has gained; secondly, as to hov much of these 

 substances the soil has lost, that is, how much it has given to the plant. The dif- 

 ference is due either to the air or to the water. This comes in to equalize the 

 account, and in fine, to settle the balance of profit and loss. 



The application of this method, as vigorous in conception as it is difficult in ap- 

 plication, has revealed a primary fact of the same order as the decomposition of 

 carbonic acid. All plants have acquired an excess of hydrogen that comes nei- 

 ther from the soil, nor from the air which does not containit ; of necessity, thare- 

 fore, it must have been derived from the water. Plants therefore do not limit 

 their action to the separation of oxygen from carbon, they also disunite hydrogen 

 and oxygen, retaining the former and rejecting the latter. Tlie water was hydro- 

 gen burned. Just as the carbonic acid was cai'bon consumed ; in both cases plants 

 have destroyed the effect of combustion by restoring the combustible bodies to the 

 state in which they were before being burned. In establishing this action finally 

 exercised upon water, no success has yet been attained in the knowledge of when 

 it is effected, and in what organs it is accomplished. 



A second consequence follows from the analyses of M. Boussingault, namely, that 

 every plant at maturity has gained gome nitrogen which betakes itself principally 

 to the seeds ; as this nitrogen may come either from the air, which holds it in a 

 free stale, or from the manures mixed with the soil, it was necessary to inaugurate 

 special experiments in order to determine its origin. M. Boussingault set to work 

 iu the following manner : at first he sowed some clover in soil exclusively consti- 

 tuted of calcined sand, which alone was intended to furnish the growing plant 

 with mineral matter, and with pure water by which the sand was moistened; as 

 for nitrogen, note was contained in it. Under these exceptional conditions the 

 clover, nevertheless, accomplished all the stages of its growth, and finally 

 acquired a feeble but certain proportion of nitrogen which necessarily must have 

 come from the atmosphere. Artichokes gave the same result with greater degree 

 of nicety. When ripe they contained twice as much nitrogen as the seeds from 

 which they sprung; but when it was attempted to reproduce the experiment with 

 cereals, and especially with wheat, the result was thut the nitrogen of the seed 

 was tenaciously preserved, but in no degree augmented. 



In every case the growth of the plant was extremely difficult, none of them 

 having that healthy aspect exliibited by them in a rich soil ; the artichokes, how- 

 ever, suffered less than the clover, and it again less than the wheat which could 

 not even develope ripe grains. The reason of this is evident, nitrogen was want- 

 ing ; all plants require it, wheat must have it, and when they do not find it in the 

 soil they languish and frequently die. Finally to confirm this conclusion, M. 

 Boussingault subjected to a comparative test three plants of the Sunflower (Helian- 

 thus) set in three similar pots filled with pure sand and moistened with pure 

 water. To the firtt no manure was given, to the second 8 centigrams (1.2344 of 



