64 Transactions British Mycological Society. 
side of the bulb. Now turn the flask so that its axis gradually 
assumes a direction parallel to that of the incident rays. During 
this turning movement one can observe that the spot of light 
gradually moves down the side of the bulb until finally it takes 
up a perfectly symmetrical position on the cotton wool plug, 
the plug thus again becoming brilliantly illuminated. 
(4) To show that if the cell-sap in the subsporangial swelling 
were replaced by air, the swelling would not act as a lens. Hold 
the flask in the beam of light as described in the first experi- 
ment. The light is refracted on to the cotton wool plug. Remove 
the water from the flask without removing the plug. Now hold 
the flask in the beam of light in the same position as before. 
The light is no longer refracted on to the plug. 
Pilobolus lives in fields, etc., on the dung of herbivorous 
animals. By directing its guns toward the source of the brightest 
light, it is enabled to shoot its sporangia into open spaces and, 
therefore, away from the dung masses and on to grass and other 
herbage. The sporangia are very adhesive and, especially after 
they have dried, stick tightly to whatever they have struck. 
Heavy rain storms do not dislodge them. Herbivorous animals 
eat grass and sporangia together. The spores pass through the 
alimentary eanal of cattle and horses unharmed and germinate 
in the solid excreta as soon as they have been dropped. 
In the heliotropic reaction of Pilobolus which is caused by 
the asymmetrical position of a spot of light we have a clear 
proof of the theory, first suggested by Haberlandt*, that helio- 
tropic reactions may take place in plants through ocellus action. 
The sporangiophore of Pilobolus, as far as I am aware, is the 
only ortho-heliotropic plant organ known which takes up its 
positively heliotropic position owing to the possession of a 
special light-perceiving cell structure. 
Pilobolus may be well described as a fungus with an optical 
sense organ or simple eye, and in using its eye for laying its 
gun, it appears to be unique in the plant world. 
The above is an abstract of a paper read December 10, 1920, 
at Guelph at the second annual meeting of the Canadian Branch 
of the American Phytopathological Society and again on 
December 28 at Chicago before the Physiological Section of the 
Botanical Society of America. On the latter occasion the model 
described in the abstract was successfully used to demonstrate 
the lens effect of the subsporangial swelling to a large audience. 
A fuller description of my observations, accompanied by illus- 
trations, is in preparation for the press. 
The University of Manitoba, Winnipeg, 
February Ist, 1921. 
* G. Haberlandt, Die Lichtsinnesorgane der Laubblatter, Leipzig, 1905. 
