ON THE PILOBOLIDvE. 
257 
which covered the surface of the water of a glass in which 
he had been growing that Alga, and a friend of his found the 
same on the mud of the Oder. But the most frequent 
habitat is the dung of various animals, as of horse, cow, 
sheep, pig, deer, elk, roebuck, rabbit, cat, goat, dog, goose, 
all of which are mentioned by various authors, and even the 
excrement of man himself. 
§ 4.—Pilaira. 
Pilobolus is one of the highest types of the Mucorini. 
Its distinguishing feature is the basal septum, without which 
the tension necessary to the projection of the sporange could 
scarcely be attained. It may be called a tliree-celled plant, 
as distinguished from most other Mucorini, which are, indi¬ 
vidually, essentially only two-celled, although, of course, this 
is only partially true. In the genus to which we now proceed, 
Pilaira, which forms an exact connecting link between Pilo¬ 
bolus and the Mucoridae, the general structure, especially of 
the sporangium, is the same, but with one important difference. 
The septum at the base of the stem is wanting; the stem is 
merely an erect branch of the mycelium and is continuous 
with it. In correlation with this difference we find that there 
is no swelling at the top of the stem, and that the sporange 
is not explosively projected. This furnishes a new proof of 
the truth of that theory of the cause of the projection which 
has been given above. 
The sporange of Pilaira has the same thickened black 
upper hemisphere as Pilobolus, and the same diffluent zone. 
The dehiscence therefore takes place in the same way. The 
interstitial gelatinous substance swells up, on the application 
of moisture, to even a greater extent than in Pilobolus. But 
the sporange is not projected. We conclude, therefore, that 
the cause of the projection in the former case lies in the 
points of difference between the two genera ; and these are 
precisely the absence of the swelling and of the septum. 
But still the species of Pilaira hitherto described secured 
a certain amount of dissemination of their spores in another 
way. The cylindrical stems rise to a considerable height, in 
Pilaira Cesatii reaching even four or five inches, and when 
mature become flaccid and quietly deposit their sporangia 
at a greater or less distance. But in a new species described 
in the sequel, the stem does not attain so great a height, 
being at first usually from ^-tli to -^th of an inch, and thus 
it is deprived of both those means by which its allies disperse 
their spores. 
