THE PILOBOLUS GUN AND ITS PROJECTILE 49 



February 13, 1929, fresh horse-dung balls taken from a stable were 

 spread over about three square feet of the chamber floor. Four 

 days later, upwards of twenty thousand fruit-bodies of Piloholus 

 longipes had appeared — every dung ball was covered with them. 

 At 2 P.M. I put my ear to the glass wall of the chamber nearest to 

 the source of daylight, and I could hear more than one hundred 

 sporangia strike the glass per minute. This miniature bombard- 

 ment had been in progress for some time and it persisted through 

 the mid-day hours until every Pilobolus gun had exploded. 



Still other cultures were made by placing dung-balls in large 

 crystallising dishes (10 X 3 inches) each covered with a glass plate 

 (c/. Fig. 26, A, c, p. 64). A slight space was provided between 

 each dish and its plate, so as to permit deleterious gases emanat- 

 ing from the dung to escape from the chamber and fresh air to 

 enter. 



It was observed that dung-balls which produced Mucors freely 

 usually produced but relatively few Piloboli, and vice versa, and also 

 that promising-looking crops of Piloboli were sometimes utterly 

 ruined by the attacks of parasitic moulds of which one sj^ecies proved 

 to be Syncephalis nodosa.^ 



The natural cultures of Pilobolus just described were so successful 

 that they were used to provide the supply of normal mature fruit- 

 bodies required for the study of (1) the structure, heliotropism, and 

 explosion of the Pilobolus gun and (2) the structure and character- 

 istics of the Pilobolus projectile. 



A iew pure cultiu-es were also made. Sporangia of Pilobolus 

 longvpes were caught on sterilised slides or cover-glasses and then 

 sown on sterilised horse dung in a large crystallising dish covered 

 with a glass plate. The spores germinated, and, after a few days, a 

 crop of fruit-bodies began to appear. Similar results were obtained 

 when sporangia or isolated spores were sown on sterilised dung- 

 agar ^ in Petri dishes. The pure cultures on horse dung were 

 employed merely for the study of the production of abnormal 

 fruit-bodies {vide iyifra), while the dung-agar cultures were used 

 to permit of observations on the germination of the spores, the 



1 Cf. p. 21. 



2 For the technique of making dung-agar vide Vol. IV, 1931, pp. 195-197. 



VOL. VI. E 



