the Development of the Theca, and on the Sexes of Mosses. 505 



the same size as the mass of granules before it had contracted (Tab. 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. I am 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 (Tab. 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 

 (Tab. 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 (Tab. 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 (Tab. XXXV. fig. 7«-)> 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 (Tab. XXXV. 

 fig. 1.) are an instance in which the strongest acid seems 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 (Tab. XXXV. fig. 3.) and discharge 

 their contents in the mass (Tab. 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. Tab. XXXV. 

 fig. 5. represents an unruptured 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 untU 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 merit of priority,) I liave long entertained the opinion that all single peristomes are in 

 reality double, but in a state of cohesion ; and 1 find that sulphuric acid, in the case of Toriula 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. 



