RECENT BOTANICAL INVESTIGATIONS.
It is commonly said that there is a great difference between the transpiration and evaporation of water in plants. The former takes place in an atmosphere saturated with moisture, it is influenced by light, by an equable temperature, while evaporation ceases in a saturated atmosphere. M. Leclerc has very carefully examined this question, and he concludes that transpiration is only the simple evaporation of water. If transpiration is more active in the plant exposed to the sun, that is due to the heat rays, and in addition arises in part from the fact that the assimilating action of chlorophyl heats the tissues, which in turn raises the temperature and facilitates evaporation.
As to transpiration taking place in a saturated atmosphere, it is a mistake; generally there is a difference in the temperature of the plant and the air, and the air is not saturated in its vicinity. In a word, transpiration and evaporation is the same thing.
Herr Reinke has made an interesting examination of the action of light on a plant. He has permitted a pencil of sun rays to pass through a converging lens upon a cell containing a fragment of an aquatic plant. He was enabled to increase the intensity of the light, so that it should be stronger or weaker than the direct sunlight. He could thus vary its intensity from 1/16 of that of direct sunlight to an intensity 64 times stronger. The temperature was maintained constant.
Herr Reinke has shown that the chlorophyl action increases regularly with the light for intensities under that of direct sunlight; but what is unexpected, that for the higher intensities above that of ordinary daylight the disengagement of oxygen remains constant.
M. Leclerc du Sablon has published some of his results in his work on the opening of fruits. The influences which act upon fruit are external and internal. The external cause of dehiscence is drying. We can open or shut a fruit by drying or wetting it. The internal causes are related to the arrangement of the tissues, and we may say that the opening of fruit can be easily explained by the contraction of the ligneous fibers under drying influences. M. Leclerc shows by experiment that the fibers contract more transversely than longitudinally, and that the thicker fibers contract the most. This he finds is connected with the opening of dry fruits.
Herr Hoffman has recently made some interesting experiments upon the cultivation of fruits.
It is well known that many plants appear to select certain mineral soils and avoid others, that a number of plants which prefer calcareous soils are grouped together as calcicoles, and others which shun such ground as calcifuges. Herr Hoffman has grown the specimen which has been cited by many authors as absolutely calcifugic. He has obtained strong plants upon a soil with 53 per cent. of lime, and these have withstood the severe winter of 1879-1880, while individuals of the same species grown on silicious ground have failed. This will modify the ideas of agriculturists, at least in regard to this plant.
Herr Schwarz has been engaged in the study of the fine hairs of roots. According to this author, there is a maximum and minimum of humidity, between which there lies a mean of moisture, most favorable for the development of these capillary rootlets, and this amount of moisture varies with different plants. He finds that this growth of hair-like roots is conditioned upon the development of the main root from which it springs. In a weak solution of brine these fine roots are suppressed, while the growth of the main root is continued. The changes of the milieu lead to changes in the form of the hairs, rendering them even branched.
Signor Savastano has ventured to criticise as exaggerated the views of Muller, Lubbock, and Allen on the adaptation of flowers to insects, having noticed that bees visit numbers of flowers, and extract their honey without touching the stigmas or pistils. He has also found them neglecting flowers which were rich in honey and visiting others much poorer. These observations have value, but cannot be considered as seriously impairing the multiplied evidences of plant adaptation to insect life.
Mr. Camus has shown that the flora of a small group of hills, the Euganean Mountains, west of the Apennines and south of the Alps, has a peculiar flora, forming an island in the midst of a contrasted flora existing about it. Here are found Alpine, maritime, and exotic plants associated in a common isolation.--Revue Scientifique.