Émile Alglave

“ Comparing this analysis with that of the lilac-leaves which were gathered at the same time, but in a city-garden, we see that those which had plenty of air, growing in the country, remote from aggregations of human beings, are the richer in nitrogenized substances. They also grow thicker and larger, the activity of respiration developing their vitality, and promoting the growth of the organs which discharge that function. Hence it would appear that, for plants, as for animals, an abundant absorption of pure air, rich in oxygen, is the essential condition of a strong, vigorous constitution. ”

“ Finally, we may conclude, from all the analyses and experiments we have here detailed, that there exist in plants, at every stage of their life, two distinct functions having different centres of action. The one is respiration, which depends upon the nitrogenous organic bodies. The other is assimilation of carbon, which has its seat in special organisms, formed principally, if not exclusively, of ternary elements. ”

“ During the growth of the leaves, the relative proportion of nitrogenized matter in their tissue grows rapidly less. It is at the maximum just when these organs are breaking out of the bud, and it goes on decreasing thenceforward till about the beginning of July, when the fruit of the lilac has been formed. From that time on, the quantity of nitrogenized matters varies but little, though it seems to gain a little in leaves approaching maturity. Finally, it is at the minimum when the process of vegetation is complete. ”

“ They respire by means of their nitrogenous constituents; 2. They assimilate carbon by means of the carbonaceous matters organized in their tissues, i. e., the chlorophyll.
This act of respiration, as we have seen, becomes less apparent as the plant begins to assimilate carbon, but, in reality, it goes on uninterruptedly, being only masked by the increased activity of the other function. That this is the case may be proved experimentally.
In the first place, we know that plants cannot live in an atmosphere without oxygen. ”

“ It will be at once observed that the absolute amount of nitrogenized substances differs widely as between the leaves of the two plants: there is at first far more in those of the maple than in those of the lilac, and this superiority is maintained during the whole period of vegetation. ”

“ It almost entirely disappears from the tissue of annual plants at the end of their growth, being condensed 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 evolution of leaves. ”

“ It is at the maximum intensity when the plant is under the direct action of the sun's rays, and gradually diminishes in importance in proportion as the light grows feebler; for instance, when the sky is overcast with clouds, and when the weather is thick and rainy. ”

“ Plants, it was held, grow in order to supply animals with food, and to make life possible for them; the activities of vegetal life produced the immediate principles of food, and animal life destroyed them ”

“ The point at which plants cease perceptibly to give out carbonic acid in the daytime varies widely according to the species. Corenwinder has found some which exhibit this property for a long time, while others lose it very early. In the first category we may class a perennial plant common in our gardens, Diclitra spectabilis, and in the second the young leaves of the beet. ”

“ Probably were we to examine from this point of view a large number of plants, we should find differences as great as these. Even between trees of the same species similar differences occur, according to their age and vigor, and more particularly according to the surroundings. ”

“ According to their behavior under these circumstances, he divides them into two categories, viz., those which vegetate in such an atmosphere only for a few days, and those which live and even flourish there for a certain length of time. ”