the Development of the Theca, and on the Sexes of Mosses. 505 
the same size as the mass of granules before it had contracted (Tas. XXXV. 
fig. 8.). This sac is so extremely pellucid, that it requires an excellent lens 
and of great power to exhibit it, and the observer will perhaps have to examine 
many masses of granules before he will find one inclosed in this sac. Iam at 
a loss to account for the fact of so few of the masses exhibiting the sac, unless 
it be that the sac is ruptured by the contraction of the granules, Many of the 
sporules will not evacuate their contents by the action of the acid; and the 
same contraction of the mass of granules takes place in these, although, from 
being surrounded by the outer coat of the sporule, the delicate internal sac 
cannot be seen (Tas. XXXV. fig. 7.)*. The empty shell of the sporule is 
dotted all over on its outer surface with minute brick-red coloured particles, 
which become of a more dingy colour the longer they are exposed to the acid 
(Tas. XXXV. fig. 4 & 7.). After the sporule is evacuated, or even when not 
empty, if it has been exposed a short time to the action of the acid, the pro- 
jection which was mentioned before (Tas. XXXV. fig. 2.) may be ascertained 
to be more transparent than any other part of the surface, and to be marked 
by three radiating lines (Tas. XVXV. fig. 7 a.), which, I presume, indicate the 
point of attachment to the three other sporules that formed the tetrahedral 
union in the young state. The sporules of Orthotrichum striatum (Tas. XXXV. 
fig. 1.) are an instance in which the strongest acid seeins scarcely to have suf- 
ficient power to rupture the outer coat, for it is only after a little maceration 
in the acid that a few of them are ruptured (Tas. XXXV. fig. 3.) and discharge 
their contents in the mass (Tak. XXXV. fig. 4). The contents of these spo- 
rules are very much contracted by the acid before their expulsion, but imme- 
diately expand to their original size on gaining their liberty. Tas. XXXV. 
fig. 5. represents an unruptared sporule after a maceration of twenty-four 
* This is not the cause of the internal sac being concealed; for I find upon washing the sporules 
free from the acid and adding diluted spirit, that the internal sac becomes visible; from which I con- 
clude, that the sac was in close apposition with the outer coat until the contracting influence of the 
spirit on the membrane separated it. 
In the course of these experiments I have ascertained that sulphuric acid is a valuable agent in the 
analysis of the peristomes of Mosses. In common with my friend Mr. Wilson, (who, however, is en- 
titled to the megjt of priority,) I have long entertained the opinion that all single peristomes are in 
reality double, but in a state of cohesion ; and I find that sulphuric acid, in the case of Tortula rigida, 
the only instance I have tried, destroys this cohesion, causing the hitherto supposed single peristome 
to split up into an internal and external layer, the former of which is nearly white and the latter red. 
