THE RESPIRATION OF PLANTS. 



65 



acid. But we have still to inquire why it is that the exhalation of 

 carbonic acid gradually diminishes as the leaves grow in size. This 

 is the great point to settle. Inasmuch as the respiratory organ grows 

 in vitality and in size, it looks as though the respiration ought to be- 

 come more active, and consequently augment the exhalation of carbonic 

 acid, if this latter process is the respiration. 



In order to solve this problem, M. Corenwinder judged it necessary 

 to investigate very closely the variations occurring in the chemical 

 composition of leaves during their vegetation. For this purpose he 

 has made numerous researches, whereof we will describe two experi- 

 ments made during the summer of 1873, one upon a white lilac, the 

 other upon a maple with fine green leaves. These occupy a good, 

 airy site in the author's garden, near the city of Lille. 



M. Corenwinder gathered leaves of these plants at suitable inter- 

 vals, from April 15th till October 31st, analyzing them afterward to de- 

 termine the amount of water, nitrogenized substances, ash, and ternary 

 compounds, they respectively contained. In sundry cases, at the most 

 characteristic periods, the proportion of phosphoric acid contained in 

 the ash was accurately weighed. 



As every one knows, water forms a considerable portion of the sub- 

 stance of leaves, as much as four-fifths. As a rule, this proportion be- 

 comes less as the season advances, and the leaves grow older, but the 

 diminution is not regular. As M. Corenwinder has shown, it needs 

 but to rain for a little while to very sensibly raise again the propor- 

 tion of water in leaves. These variations in the water of vegetation 

 of leaves make it difficult to compare the other elements which they 

 contain, and hide the relative increase or decrease of each of these ele- 

 ments. De Saussure evaded this difficulty by calculating the leaves 

 in the dry state, and then determining what would be the relative 

 proportions per cent, of the various elements in each leaf, if really de- 

 prived of all its water. M. Corenwinder adopts the same course. 

 Having given in full the results of his two series of exjjeriments, he 

 condenses them in the following tables, which enable us easily to fol- 

 low the evolution of each of the groups of elements in the leaf: 



LEAVES OF COMMON" LILAC. 



1873. 



VOL. VI. 5 



