TURGIDITY 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. 1 



V. THE NATURE OF THE OSMOTICALLY 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 2 

 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 KC1 and KNO 3 play important rCles in the 

 maintenance of turgor in leaf -stalks of Gunnera scabra and 

 the shoots of Helianthus tuberosus, respectively. Copeland 3 

 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 5 found that in many plants organic acids are 

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

 The research of von Mayenburg 6 shows that Aspergillus 



i On the action of animal membranes in diffusion phenomena see the following : 

 H. J. HAMBURGER, " Die isotonischen Koeffizienten und die rothen BlutkOrperchen," 

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

 intra-abdominalen Druckes auf die Resorption in der BauchhOhle," Arch. f. Anat. 

 u. Physiol., Physiol. Abth., Jahrg. 1896, p. 302, ibid., p. 428; G. KOVESI, "Beitrage 

 zur Lehre der Resorption im Diinndarm," Physiol, Centralbl., Vol. XI (1898), pp. 

 555-7 and 593-7 ; O. COHNHEIM, "Ueber Dunndarmresorption,"ZettecJir./. Biol., Vol. 



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

 bran auf die Diffusion verschiedener KOrper," Pflugers Arch. f. d. ges. Physiol. , 

 Vol. LXXVIII (1899), pp. 205-61 ; R. HOBER, " Ueber Resorption im Dunndarm," ibid., 

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

 G. FLUSIN, "Sur Tosmose & travers la membrane de ferrocyanure de cuivre," 

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



2H. DE VEIES, "Eine Methode zur Analyze derTurgorkraft,"7aftrb./. wiss.Bot., 

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



3E. B. COPELAND, "The Relation of Nutrient Salts to Turgor," Bot. Gaz., Vol. 

 XXIV (1897), pp. 399-416. 



*G. KK&us,Stoffwechsel der Crassulaceen, 1886. 



5H. DEVRIES, "Ueber d. Bedeutung d. Pflanzensauren," etc., Bot. 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 MAYENBURG, " LOsungsconcentration und Turgorregulation bei den 

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



