254 
ON THE PILOBOLID.E. 
lieliotropic, and bend energetically towards the side from 
which the light proceeds, if grown before a window. I have 
grown P. Kleinii in a dark room, to which only a feeble ray of 
light penetrated through a narrow crevice, and under these 
circumstances the stem was very much drawn up, being 
sometimes three-quarters of an inch in length or more, 
though its ordinary height is under one-tenth of an inch. 
But the diameter of the stem was then much less than usual, 
the swelling was attenuated, and the whole fungus almost 
colourless, except for the spores and the black cap. This 
property of heliotropism is not universal among Fungi ; it is 
possessed by some, but not all, species of Mucor, while some 
of the allied genera are altogether wanting in it. M. Woronin 
records an interesting experiment which he performed on 
Sordaria Jimiseda* The neck of the perithecium of this 
species bends towards the light, and, by growing it in light 
proceeding from one side only, and turning it round at 
intervals, the neck may be made to form itself into a zigzag 
(or spiral), changing its direction three or four times. All 
the species of Pilobolus seem to be affected in the same way, 
and I have often caused the stem to grow with a double 
curvature, by turning round the plate on which it stood before 
a window. 
m. —Periodicity of Growth. 
Another point deserving of consideration in the physiology 
of Pilobolus is the duration of its growth. It is the Ephemeron 
of plant life. Each individual stem lasts, under normal con¬ 
ditions, only one day. But what is still more surprising is 
that it goes through its various stages with almost the 
regularity of clockwork. Each afternoon, about 3 p.m., the 
surface on which it is growing is studded with a number of 
minute subulate yellow points ; these are the young stems. 
By 5 p.m. the sporangia begin to form. During the evening 
the upper septum is completed, the cap of the sporangium 
assumes a darker colour, passing through olive to dark brown; 
at the same time the swelling begins to appear. Then during 
the night the spores are completely elaborated, the cap assumes 
its ultimate thickness and blackness, and the swelling reaches 
its full size. Early the next day, the surface, which last 
night we had left covered with a number of tiny black-lieaded 
pins, is seen sprinkled as it were with diamond dust, each 
swelling brilliantly glittering in the beams of the morning sun. 
This, however, is a sight reserved for the “ early bird.” As 
* “ Beitrage zur Morph, und Pliys. der Pilze,” ser. iii., pp. 9, 10, 
pi. ii., figs. 12, 11; pi. iii., fig. 7. 
