ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 255 



tLat wliicli serves as a mechanical transport of material and passes 

 Bnclianged through the plant. It may therefore be compared to the 

 perspiration of animals, and is intimately connected with the process of 

 oxidation within the plant. 



It results from this hypothesis that the transpiration from the leaf 

 per unit of surface must be less, the less active the internal activity of 

 growth, or, in other words, the larger the amount of surface which goes 

 to the production of a given weight of dried substance. The correctness 

 of this view was proved by the following experiments : — Young seed- 

 ling cucumbers, 10 cm. long and of an average weight of 1*5 g., were 

 each placed on June 14 in a vessel of two litres capacity, containing 

 1700 g. of leaf-mould, and 400 g. water. On July 17, the plants had 

 an average leaf-surface of 1700 g., and had transpired 454 g. water. 

 Five fully developed leaves were now removed from one plant, having 

 a superficies of 525 • 2 sq. cm., and a weight of 9 • 42 g. These plants, 

 from which one-half of the leaf-surface had now been removed, main- 

 tained the same amount of transpiration as the uninjured ones, showing 

 that the surface which remained must have performed a portion of the 

 work of the leaves that had been removed. On August 3 a still further 

 quantity of leaves with a superficies of 88*8 sq. cm. and a weight of 

 8 • 2 g. was removed. Since the first denudation the plant had grown 

 very quickly, having formed 10 leaves with a superficies of 1121 • 79 

 sq. cm. At the same time 16-2 g. were removed from a second 

 plant, having a superficies of 264" 1 sq. cm. After fourteen days 

 the amount of transpiration was again nearly the same from all the 

 plants. Those which had been denuded showed no decrease of trans- 

 piration, the substance removed being replaced by a rapid fresh pro- 

 duction of leaf-surface. A second series of experiments gave similar 

 results. 



Transpiration was also shown to be dependent on the concentration 

 of the nutrient solutions. Experiments were made on four different 

 species of cereals, with five different concentrated solutions, and the 

 transpiration was found to be less in proportion to the concentration of 

 the fluid. With those solutions in which the plant grew most rapidly, 

 the absolute amount of transpiration was large, as was the general 

 metastasis, but the relative proportion to the weight of newly formed 

 substance was very small. 



The following is Sorauer's explanation of these phenomena. A 

 maximum transpiration accompanies the rapid production of substance 

 in an optimum nutrient solution. But for this fresh production a 

 certain quantity of mineral constituents is indispensable, and these are 

 absorbed by the roots out of the fluid. When this solution is very 

 dilute, a larger quantity of water must be carried up ; and thus, with 

 the increase of the mechanical water of transpiration, the total quantity 

 of water transpired increases above the optimum with the decreasing 

 concentration of the fluid. 



Easily Oxidizable Constituents of Plants.* — It is a well-known 

 fact that the juices of many plants become discoloured on exposure to 



* Zeitschr. Physiol. Chem., vi. (1883) pp. 263-79. See Journ. Chem. Soc — 

 Abstr., xliv. (188.B) pp. 880-1. 



