28 RESEARCHES ON FUNGI 



that the formation of drops on the sporangiophore, hke the forma- 

 tion of drops on the epidermis of nectaries, is due to a substance 

 which issues from the cell-walls and by osmosis attracts water to 

 itself. 1 Having observed that there is a most plentiful discharge 

 of water from the sporangiophore and that the excretion of water 

 from the sporangium at the time of ripening of the spores is small 

 or has entirely ceased, Lepeschkin refused to accept the view of 

 Brefeld according to which the excretion of water is due to the 

 protoplasm becoming denser during the formation of the spores. ^ 

 Of the two hypotheses of Pfeffer, (1) that the excretion of water in 

 a cell is due to the unequal distribution of osmotic substances in the 

 vacuole, water being absorbed where osmotic substances are in 

 greatest concentration and excreted where the osmotic substances 

 are in least concentration, and (2) that the excretion of water is due 

 to the unequal permeability of the protoplasmic membrane for 

 water and dissolved salts, water being absorbed where the membrane 

 is less permeable and best able to withstand osmotic pressure and 

 excreted where the membrane is more permeable and least able to 

 withstand osmotic pressure, Lepeschkin accepted the latter. ^ He 

 concluded that the facts elucidated by his investigations justify the 

 conclusion that water excretion in Pilobolus is due to the difference 

 in permeability of the plasma-membrane for dissolved substances 

 in its upper and lower parts, and that all the phenomena caused by 

 the action of anaesthetics, poisonous substances, temperature, and 

 strong light are due to the great changeableness of the plasma- 

 membrane in respect to permeability.* 



That differential permeability may lead to excretion of drops 

 seems to be proved by some experiments of Weis ^ who lowered the 

 permeability of one part of a cell by means of alcohol. Weis sub- 

 jected one half of a long (30-50 mm.) intact internodal cell of 

 Nitella to alcohol vapour or bathed it in a 10 per cent, alcohol 



with a brush removes a coat of fat from the exterior of the sporangiophore, that such 

 a washed sporangiophore excretes water, and that the excreted water instead of 

 forming drops runs at once over the surface of the cell-wall. 



1 W. W. Lepeschkin, loc. cit., pp. 419-421. ^ /jj^/., p. 421. 



3 Ibid., pp. 421^25. " Ibid., pp. 434^35. 



^ A. Weis, " Zur Mechanik der Wasserausscheidung aus lebendcn Pflanzenzellon." 

 Planta, Bd. II, 1926, pp. 241-248. 



