TUEGIDITY 83 



yet been shed. In the realm of pure physical chemistry 

 there is some evidence that osmotic membranes may some- 

 times play a chemical part.' 



V. THE NATUKE OF THE OSMOTIOALLT ACTIVE SOLUTES 



Within the cell sap there are very many substances in solu- 

 tion, and thus the question as to what substances the turgor 

 pressure is due becomes of some importance. DeVries^ 

 found that in the onion bulb-scale and in the beet root this 

 pressure is chiefly due to stored sugar. He also showed 

 that the salts KOI and KNO3 play important rSles in the 

 maintenance of turgor in leaf -stalks of Gunnera scabra and 

 the shoots of Helianthus tuberosus, respectively. Copeland' 

 concluded from experiments with Phaseolus, Pisum, Fago- 

 pyrum, and Zea, that in these plants the osmotically active sub- 

 stance is mainly potassium nitrate. On the other hand, Kraus* 

 and DeVries'^ found that in many plants organic acids are 

 the main source of the osmotic pressure of the cell sap. 

 The research of von Mayenburg* shows that Aspergillus 



1 On the action of animal membranes in diffusion plienomena see the following : 

 H. J. Hamburger, " Die isotonischen KoefiEizieuten und die rothen BlutkOrperchen," 

 Zeitschr. f.physik. Chem., Vol. VI (1890), pp. 319-33; idem, "Ueber den Einfluss des 

 intra-abdominalen Druckes auf die Besorption in der BauohhOhle," Arch. f. Anat. 

 u.. Physiol., Physiol. Abth., Jahrg. 1898, p. 302, ibid., p. 428; G. KOVBSI, "Beitrage 

 zur Lehre der Besorption im Dttnndarm," Physiol. Centralbl., Vol. XI (1898), pp. 

 555-7 and 593-7 ; O. Cohnheim, "Ueber Dflnndarmresorption,"ZeJfecAr./. Bio!., Vol. 



XXXVI (1898), pp. 129-53; S. G. Hedin, " Ueber den Einfluss einer thierischen Mem- 

 bran auf die Diffusion verschiedener KOrper," Pflilgers Arch. /. d. pes. Physiol., 

 Vol. LXXVm (1899), pp. 205-61; E. HObee, " Ueber Besorption im Dflnndarm," ibid., 

 Vol. LXXIV (1899), pp. 246-71. On the action of the copper ferrooyanid membrane see 

 G. Flusin, "Surl'osmose h travers la membrane de ferrooyanure de cuivre," 

 Campt. rend.. Vol. CXXXII (1901), pp. 1110-12. 



2 H. De Veies, " Eine Methode zur Analyze der Turgorkraf t," Jahrb.f. vriss. Bat., 

 Vol. XIV (1884), pp. 427-60. 



3E. B. COPBLAND, "The Belationof Nutrient Salts to Turgor," Bot. GFo«., Vol. 

 XXIV (1897), pp. 399^16. 



*Q. K-RKVa, Staff wechael der Crassulaceen, 1886. 



6H. DeVbibs, " Ueber d. Bedeutung d. Pflanzensauren," etc., So*. Zeitg.,'Vol. 



XXXVII (1879) , pp. 847-53 ; idem, " Ueber d. Antheil Pflanzensauren," etc., Bot. Zeitg., 

 Vol. XLI (1883), pp. 849-54. 



6 O. H. VON Mayenbdeg, " LOsungsconcentration und Turgorregulation bei den 

 Schimmelpiken," Jahrb.f. wiss. Bot., Vol. XXXVI (1901), pp. 381-420. 



t/ 



