388 
ON THE PILOBOLIDjE. 
3.—PILAIRA DIMIDIATA, milii. 
Pilobolus anomalus, Brefeld, l.c. pro parte (1881). 
Pilaira inosculans , milii, ohm, “ Mid. Nat.,” vi., 119 (1883). 
Pilaira dimidiata, Grove, “ Journ. Bot.,” p. 132, pi. 215, f. 7 (1884). 
P. stipite curto, gracili, asquali, apice denique nutante; 
sporangio primo flavido, demum nigro; columella leviter 
colorata, convexa, prope sequatorem vesiculse apicalis inserta, 
ifcaque apopliysin magnam liyalinam prsebente, ubi adest in 
fnngo vegeto constrictio profundula ; sporis liyaliuis, dilutis- 
sime flavidis, elliptico-oblongis, 12-14/^x 5-Qu. (PI. vi., 
%. 10 .) 
Stem ^-1 mm. liigh, when the sporange becomes black; afterwards 
increasing to 3-4 mm. Sporange - 10-'12 mm. in diameter. Distinguished 
from P. Cesatii, not orly by its much smaller size, but also by its 
peculiar apophysis, which is almost as large as the sporange, but 
slightly less in diameter and not granular. It can scarcely be a badly 
nourished form of P. Cesatii, as it grew luxuriantly on a rich substr turn. 
On dog’s dung. March, April. 
England; rare. Met with in one locality only, Worcestershire. 
Tills concludes the known species of Pilobolidae. It will 
be seen that tliey form a close series, which, taken in con¬ 
junction with the Mueoridae, clusters around two points, 
Pilobolus Kleinii, and Pilaira Cesatii. The affinities of the 
species, considered in the light of evolution, are very curious. 
We must suppose that a Mucor possessed, as many Mucors 
are, e. g. Mucor plasmaticus, of an abundance of the interstitial 
gelatinous substance in its sporangium, became provided with 
an upper indurated cap, and a lower diffluent zone. Many 
species of Mucorkke do show a decided difference in the per¬ 
sistence of different parts of their sporangial membrane, e.g. 
Circinella. The sporange would thereby be enabled to drop 
off its stem, with the spores included. This would probably 
be an advantage in one respect, as preserving the spores from 
adverse influences, till sufficient moisture was obtained to en¬ 
able them to germinate. 
But it would be accompanied by a drawback, in that the 
diffusion of the spores would be less complete; thus we should 
not expect the species of Pilaira to be widely spread. But 
now the faculty of intercalary growth, possessed by that portion 
of the stem of Pilaira and Mucor situated immediately 
beneath the sporangium, would vary slightly, allowing of a 
growth in breadth instead of length. If then a septum arose 
at the base, so as to permit of the attainment of sufficient 
tension in the swelling, we should inevitably arrive at the pro¬ 
jection of the sporange, in the way in which we know it to 
take place. Thus the spores would be widely dispersed. At 
the same time, the thick layer of gelatinous substance, which 
