HISTORY OF PILOBOLUS 31 



contents in different parts of the cell or to the plasma-membrane 

 differing in permeability in different places. 



In 1919, Stern ^ suggested that bleeding from wounds in flowering 

 plants is due to electro-osmosis ; and, in 1921, Blackman ^ discussed 

 electro-osmosis as a possible cause of the excretion of drops in 

 Pilobolus. Hitherto, however, the electrical phenomena which 

 accompany the excretion of drops in Pilobolus have not been 

 investigated. 



From the review of the Hterature given in the foregoing pages 

 it appears that we are still far from understanding the mechanism 

 by means of which Pilobolus excretes its drops. It is possible that 

 further hght might be thrown on the problem : (1) by measuring, 

 with the help of Barger's or Ursprung and Blum's capillary-tube 

 method,^ the osmotic pressure of a series of drops exuded from one 

 and the same point on the sporangiophore ; (2) by comparing the 

 osmotic pressure of the drops and of the cell-sap ; (3) by obtaining 

 more accurate chemical analyses of the drops and cell-sap than 

 hitherto has been attempted ; and (4) by investigating the suction 

 force of the basal swelling and of the subsporangial swelling by the 

 method used by Ursprung and Blum * in their measurements of the 

 difference in the suction force exerted through opposite walls of 

 endodermis and other cells. 



^ K. Stem, " Uber elektroosmotische Erscheinungen und ihre Bedeutung fiir 

 pflanzenphysiologische Fragen," Zeit. f. Botanik, Bd. XI, 1919, p. 600. 



^ V. H. Blackman, loc. cit., p. 114. He cites the work of Bartell and Madison 

 who found that with various solutions the normal osmotic tendency of gold-beaters' 

 skin membranes might be increased, decreased, or reversed. " The results can be 

 explained by the electrical relations of the membrane ; a difference of potential 

 between the faces of the two membranes is developed if electrolytes are used and this 

 electro -endosmosis may aid or retard the normal process of osmosis ; we thus have 

 an additional force superimposed on the ordinary osmotic relations." Among the 

 most recent papers treating of electro -osmosis through organic membranes with 

 numerous citations of the relevant literature is that of L. Bruner, " Untersuchungen 

 iiber die Elektrolyt-Permeabilitat und Quellung einer leblosen natiirlichen Mem- 

 brane," Jahrb.f. wiss. Bot., Bd. LXXIII, 1930, pp. 513-632. His experiments were 

 made with the testa of the Horse Chestnut. 



^ For Barger's method vide infra, pp. 141-142. For the method of Ursprung and 

 Blum, vide their " Zwei neue Saugkraft-Messmethoden," Jahrb. f. wiss. Bot., Bd. 

 LXXII, 1930, pp. 257-306. 



* A. Ursprung and G. Blum, " Eine Methode zur Messung Polarer Saugkraft- 

 differenzen," loc. cit. 



