58 THE POPULAR SCIENCE MONTHLY. 



the plant, the humidity of the soil, and the heat to which it is exposed. 

 It was proved by De Saussure that the quantity of ash is much less 

 in nascent leaves than in those which have attained the term of their 

 existence. 



4. De Saussure also proved that in the ash of buds and nascent 

 leaves there is more phosphoric acid than is found at any later stage. 

 Since his time this fact has been confirmed by Garreau, of Lille, and 

 by Corenwinder. The present series of experiments furnishes a new 

 demonstration of this important phenomenon. 



In the tables we have given the reader will observe that the pro- 

 portion of phosphoric acid, which at the outset w r as considerable, espe- 

 cially in the maple-leaves, rapidly grows less, and when the process 

 of vegetation is at an end it is very small indeed. Thus, when com- 

 ing from the bud, they contain (in the dry state) about .028 phospho- 

 ric acid; but at last they contain only about .001. It was long ago 

 proved by M. Corenwinder that the phosphorus contained in plants 

 is an essentially variable quantity. It almost entirely disappears from 

 the tissue of annual plants at the end of their growth, being con- 

 densed in the seeds, and ultimately serving to perpetuate the species. 

 In perennial plants, the phosphorus does not go into the seeds merely 

 it is also diffused through the trunk and the branches ; further, it 

 hibernates in the buds, which contain the essential elements of the 

 seed, and which perform the same functions as the latter in the evolu- 

 tion of leaves. 



V. 



Having now made the experiments tell their story, and described 

 the comparative evolution of the various elements of the leaves dur- 

 ing their annual life, let us next see whether these variations in chem- 

 ical constitution may be coupled together under a theory which shall 

 explain the modifications undergone by the gaseous exhalations of 

 plants at the various stages of their life. 



When we study closely the figures relating, for instance, to the ma- 

 ple, we find that, in the first stage of growth the nitrogenized matters 

 are very considerable. Probably they have an organization of their 

 own, and exist independently of the vegetal cells ; at all events, they 

 discharge functions which may be called animal they respire, and in 

 this early stage respiration is the dominant function. The carbonic 

 acid resulting from this operation is at first only in part retained in 

 the plant by the reducing action of the chlorophyll. The young plant, 

 when exposed to the light and placed in atmospheric air, exhales an 

 excess of carbonic acid. 



In the second period, the relative proportion of nitrogenized matters 

 grows less, while, on the other hand, the carbonaceous matters increase. 

 The plant now exhales only a small amount of carbonic acid, the latter 

 being almost entirely retained by the chlorophyll, which decomposes 

 it, and fixes its carbon. 



