140 PLANT PHYSIOLOGY 



view is questioned by Giltay,* at least so far as food- 

 manufacture is concerned. On equally fertile soil in equal 

 lengths of time, the activities of tropical and temperate 

 plants are not unlike. If this is true, there is no need of 

 more rapid absorption and transfer of food in tropical 

 plants than in those of temperate climes, and transpiration 

 may at least be no more rapid, may safely be less rapid, 

 than in dryer temperate regions. It may easily happen in 

 temperate regions that the plant takes in more water and 

 more salts than it really needs, and that while the former 

 evaporates, the latter accumulate in useless forms and 

 quantities with or without chemical change. Whether the 

 transpiration of plants adapted to the climatic conditions of 

 different parts of the world differs greatly must be regarded 

 as still unsettled', f 



The result of the evaporation of water from any solution 

 is the concentration of the solution and the lowering of 

 its temperature. With the evaporation or transpiration of 

 water from the leaves of plants, the cell-sap of the cells 

 giving off water will tend to increase in density and to de- 

 crease in temperature at a rate proportional to the rate of 

 transpiration. The increase in density of the cell-sap is ac- 

 companied by an increase in osmotic pressure, and the cell- 



* Giltay, E. Uber die vegetabilische Stoffbildung in den Tropen und in 

 Mitteleuropa. Annales du Jardin Botanique, Buitenzorg, t. XV., 1898. 



t The discussion of the question is represented by the following papers : 

 Haberlandt, G. Anatomisch-physiolog. Untersuchungen iiber das tropische 

 Laubblatt. I. Uber die Transpiration einiger Tropenpflanzen. Sitzungs- 

 ber. d. K. K. Akad. d. Wiss. zu Wien, Bd. CL, Abth. I., 1892. Uber die 

 Grosse der Transpiration im feuchten Tropenklima. Jahrb. f. wiss. Bot- 

 anik, Bd. 31, 1898. Erwiderung zu Giltay's Abhandlung. Jahrb. f. wiss. 

 Bot., Bd. 33, 1899. Stahl, E. Einige Versuche iiber Transpiration und 

 Assimilation. Botanische Zeitung, 1894. Burgerstein, A. fiber die Trans- 

 pirationsgrosse von Pflanzen feuchter Tropengebiete. Ber. d. Deutsch. 

 Bot. Gesellsch., 1897. Materialien zu einer Monographic betreffend die 

 Erscheinungen der Transpiration der Pflanzen. Verhandl. d. K. K. Zool.- 

 Bot. Gesellsch., Wien, 1901 and earlier. Giltay, E. Vergleichende Studien 

 iiber die Starke der Transpiration in den Tropen und im mitteleuropai- 

 schen Klima. Jahnb. f. wiss. Botanik., Bd. 30, 1897. Die Transpiration 

 in den Tropen und in Mittel-Europa, II., Jahrb. f. wiss. Bot., Bd. 32, 1898 ; 

 Ibid., III., loc. cit., Bd. 34, 1900; Ibid., Bot. Centralbl., Beihefte, Bd. 9, 

 1900. 



