HISTORY OF PILOBOLUS 33 



of a sporangium of Pilobolus or of the eight spores from the ascus 

 of a Peziza : (1) the turgor pressure of the cell-sap, and (2) the 

 resistance of the wall to breakage. Both in Pilobolus and in an 

 ascus the wall is so constructed that it breaks along a particular 

 Une of ultimate weakness. It is possible that shortly before dis- 

 charge the wall, along its break-hne, is gradually weakened and 

 that the turgor pressure of the cell-sap is incapable of causing dis- 

 charge of the sporangium or spores until the weakening has pro- 

 ceeded far enough. Under natural conditions, as Lepeschkin ^ 

 found, the concentration of the cell-sap of the sporangiophore of 

 Pilobolus steadily diminishes as development proceeds ; but whether 

 or not this concentration, and with it the turgor pressure, is markedly 

 increased just before the discharge of the sporangium remains to be 

 determined by experiment. 



1 have observed that the application of poisonous substances, 

 such as iodine, mercuric chloride, silver nitrate, copper sulphate, 

 sulphuric acid, acetic acid, and alcohol, to the hymenium of Peziza 

 vesiculosa (my P. repanda) lying in water at once causes the asci to 

 explode and discharge their spores. ^ It seems unlikely that the 

 discharge of the asci, which takes place within a few seconds of the 

 application of the reagents, can be due to increase of cell-turgor. 

 It was found that asci which had contracted after treatment with 

 a neutral salt may be caused to explode when brought into contact 

 with iodine.^ It is possible that the early explosion of the sporangio- 

 phores of Pilobolus in Lepeschkin's experiments with chloroform 

 and ether was in part due to the action of the anaesthetics on the 

 protoplasm immediately beneath that part of the wall which 

 eventually ruptures. It may be that this protoplasm is stimulated by 

 anaesthetics to weaken the wall through enzyme action prematurely * 



Influence of External Conditions on the Breadth of the Sub- 

 sporangial Swelling. — Lepeschkin ^ at 9 p.m. placed tufts of young 

 fruit-bodies on water and on 4 -5, 9, and 18 per cent, sugar solutions. 



^ W. W. Lepeschkin, loc. 0(7., p. 422. Lepeschkin observed that a young spor- 

 angiophore (no sporangial swelling) and a ripe sporangiophore of Pilobolus Kleinii 

 plasmolyse with a 3 • 7 and a 2 • 3 per cent, solution of potassium nitrate respectively. 



2 These Researches, Vol. I, 1909, p. 238. 



3 Ibid., p. 239. " Cf. ibid., pp. 239-240. 

 ^ W. W. Lepeschkin, loc. cit., p. 423. 



VOL. VI. D 



