220 
ON THE PILOBOLIDiE. 
their lower surface. I think that nearly every one which 
was to be found on the pieces of paper placed to receive the 
sporangia in the experiment narrated in the last paragraph 
but one, was in that position ; and it is so certainly with all 
which cling to the interior of the bell-glass. [Bell-glass and 
paper exhibited.] But there are exceptions when they fall 
on a rough surface, and it is easy to see the reason of this 
when we remember the dehiscence previously mentioned. 
The upper surface of the sporangium is round and practically 
smooth (though not actually so), and the lower edge and face 
are occupied by the gelatinous substance. Now, when a 
sporange is thrown upwards it will certainly rotate as it flies; 
if the smooth top only comes in contact with the glass (or 
other vertical surface) it will not adhere, and the sporange 
will fall down again. But, if any portion of the gelatinous 
substance touches the glass, the force of progressive attrac¬ 
tion* between it and the thin film of moisture which will 
usually cover the glass must invariably bring the lower, 
somewhat plane, surface of the sporangium into close contact 
with the glass. In the case of the paper, the sporangia 
would naturally roll over, if they fell on the convex surface, 
and settle on tlieir lower face. But if they fall on the uneven 
surface of the dung on which they grow they may be found 
in all positions, even bottom upwards. 
The stem from which the sporange has been projected 
remains for a short time still standing, and in that condition 
we can easily see the circular aperture at the top from which 
the columella was torn away (Fig. 11). We may sometimes 
find a stem without its sporange, but still retaining its 
columella; it would be a mistake, however, to suppose in 
this case that the sporange had been violently thrown off. 
It may have been accidentally removed in the manipulation 
of the specimen; it may have been, as Klein suggests, shot 
off by another passing sporange ; hut usually, I believe, the 
occurrence is to be explained by the so often mentioned 
phenomena of dehiscence. If an abundant supply of mois¬ 
ture be present the gelatinous substance swells up to an 
enormous extent, and the spore-mass, being then only lightly 
perched upon the conical columella, would obviously be liable 
to fall off by its own mere weight, unless it were very 
accurately balanced. Klein remarks that, when this has 
taken place, he has frequently seen the columella alone 
afterwards projected by the ordinary explosive action. 
* See Dr. R. Norris’s Experiments in the Proceedings of the 
Birmingham Natural History and Microscopical Society, 1869, p. 36, 
pi. viii. 
(To be continued.) 
