CHAPTER II 



PILOBOLUS AND THE OCELLUS FUNCTION OF ITS 

 SUBSPORANGIAL SWELLING 



Culture Methods — Germination of Spores, Growth of Mycelium, .and Formation of 

 Primordia of Fruit-bodies — A Colourless S^wrangial Wall as an Abnormality 

 in Pilobolus longipes — Species observed — General Description of the Pilobolus 

 Gun and its Projectile — The Discharge of the Projectile — ^Development of 

 the Pilobolus Gun and its Projectile — The Heliotropism of the Pilobolus Gun 

 demonstrated by a Simple Experiment — The Range of the Pilobolus Gun — 

 The Structure of the Sporangiophore and Sporangium illustrated by Pilobolus 

 Kleinii and P. longipes — The Two Functions of the Subsporangial Swelling — 

 The Heliotropism of the SporangiojAore with special reference to the Ocellus 

 Function of the Subsporangial Swelling — The Mechanism of Heliotropic 

 Response in Pilobolus and in the Leaves of certain Flowering Plants — The 

 Ocellus of Pilobolus and the Eye-spots of Volvox — The Ocellus of Pilobolus 

 and the Human Eye — ^A Heliotropic Experiment made on Pilobolus longipes^ 

 A Solution of the Problem of the Reaction of the Sporangiophore of Pilobolus 

 to Two Equal Beams of White Light — A Model for illustrating the Pilobolus 

 Fruit-body in its Relations with Light — The Periodicity in the Development 

 of Pilobolus Fruit-bodies — The Subsporangial Swelling and the Discharge of 

 the Pilobolus Gun — The Osmotic Pressure of the Cell-sap of Pilobolus — Factors 

 in the Efficient Working of the Pilobolus Gun — An Analysis of the Cell-sap 

 of Pilobolus longipes — The Landing of the Pilobolus Projectile and the Attach- 

 ment of the Sporangium to Herbage — The Relations of Pilobolus with Flowering 

 Plants and with Herbivorous Animals. 



Culture Methods. — At Winnipeg, during the winter months, 

 Pilobolus was usually obtained as follows. Horse-dung balls, 

 collected in the frozen condition from the streets or obtained fresh 

 from a stable, were placed unbroken in a compact layer on the floor 

 of a large culture chamber which was exposed to daylight on a table 

 in the laboratory. The chamber was 3 feet long, 1 • 5 feet wide, and 

 2 feet high, its four sides and its roof were made of glass, while its 

 floor was covered with a sheet of zinc having upturned edges. The 

 air of the chamber was kept moist by means of a standing beaker 



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