636 BOWMAN— ECOLOGY AND 



salt soil than in the sodium chloride free soil and likewise for the 

 Knop solution cultures. He finds that NaCl externally makes ab- 

 sorption through the roots difficult and that contained in the plant's 

 tissues lessens transpiration. Other workers have also experimented 

 with plants in solutions of different salts, as Burgerstein/"^ who 

 grew plants in borax solutions of one to three tenths per cent, con- 

 centration and by comparison of the transpiration of similar plants 

 in distilled water, he found that those in the borax solution trans- 

 pired much less, but an objectionable feature in those experiments 

 was the highly toxic effect of boric acid and borates, as Peligot^°^ 

 has shown, since the plants began to droop and die on the second 

 day of the experiments. 



Cuboni^^" who experimented with sprinkling branches of various 

 trees and shrubs with thin solutions of calcium hydroxide and meas- 

 uring the transpiration by photometric methods found that this sub- 

 stance had no effect, but as there was no absorption here the results 

 cannot be compared. The available water for absorption is natu- 

 rally the factor most concerned in transpiration and as the increas- 

 ing density of the solutions makes osmosis and absorption more 

 difficult the corresponding phenomenon is decreased in amount. 

 Not all salts in solution however have this physical effect, if the 

 works of Sachs"^ and Senebier"- may be considered. The effect 

 is also partly chemical, and the physical osmotic relations cannot 

 be supposed to be due to the density of the solutions alone, thus 

 Senebier, who was an earlier investigator on the subject, states that 

 aqueous solutions of sodium sulphate, potassium nitrate and potas- 

 sium tartrate occasion an acceleration in the water movement in 

 plants, while Sachs claims a retardation for ammonium sulphate and 

 sodium chloride. Both the experimenters worked with twigs and 

 so the action by root absorption is not considered and the assump- 



1"*^ Burgerstein, A., " Die Transpiration dcr Pflanzcn," p. 146, 1904. 



10^ Peligot, M., Coviptes Rciidus dc I'Acad. dcs Sci. Paris, t. 83. 



11** Cuboni, G., " La Transpirazione e TAssimilazione nella Foglie trattata 

 con Latte cli Calci, Malpighia," Vol. i, p. 295, 1887. 



^^^ Sachs, T., " Ueber den Einfluss der chemischen und physikalisclien 

 Beschafifenheit des Bodens auf die Transpiration der Pflanzen. Landw. Vers- 

 Stationen," Bd. L, 1859, P- 203. 



^^- Senebier, J., " Physiologic Vegetal," Geneve, 1800. 



