THE PILOBOLUS GUN AND ITS PROJECTILE 105 



The subsporangial swelling is capable of producing not only a 

 spot of light but also a more or less well-defined image of the source 

 of light or of an illuminated object. Such images were observed 

 under conditions which will now be described. 



A fruit-body of Pilobolus Kleinii was fixed in air over a shde 

 on the stage of a microscope, so that the long axis of the subspor- 

 angial swelling was horizontal and so that 

 the swelling was illuminated from below by 

 means of parallel rays reflected upwards from 

 a plane mirror. On looking down at the 

 swelhng, I observed on its upper wall an 

 oval spot of light like that already described. 

 When the microscope was placed at a distance 

 of fourteen feet from a window, the spot of 

 Ught was found to contain an image of the 

 window-bars ; and, when a hand was held 

 three feet in front of the microscope between 

 the mirror and the window, the spot of light 

 was found to contain a black image of the 

 hand. 



Subsequently, images formed by the sub- 

 sporangial swelhng of Pilobolus longipes were 

 photographed, and two of the photographs 

 are reproduced in Figs. 51 and 52. 



Fig. 51 shows a daylight shadow-photo- 

 graph of a hand. The microscope was pre- 

 pared by removing the condenser and turning 

 on the plane mirror. The fruit-body to be 



used to form the image, together with a Uttle dung on which it was 

 growing, was taken from a culture dish and set in a closed com- 

 pressor cell (c/. Fig. 14, Vol. II, p. 45) so that its apical portion 

 projected freely in the air in a horizontal direction. The moist air 

 of the chamber prevented the fruit-body from drying up. The com- 

 pressor cell was placed on the stage of the microscope. Daylight 

 from a window was employed. Parallel rays were reflected upwards 

 from the flat mirror to the subsporangial swelling of the fruit-body 

 in the compressor cell. The hand was held one foot in front of the 



Fig. 51.^ — Pilobolus longi- 

 pes. Photomicro- 

 graph of the image 

 of a hand. Fide text. 

 Magnification, 40. 



