HuTTON. — On Modifications in Capsules of Mosses. 347 



[a.) In some European mosses, such as Gymnostomum curvirostrum, Pottia 

 truncata (fig. 1), P. heimii, amd Stylostegium ccBspiticum, the operculum adheres 

 to tlie columella, wlaicli elongates when the spores are ripe and lifts up the 

 operculum. Some mosses even which have peristomes have also the operculum 

 adhering to the columella, such as Dissodon hornschuchii, from Europe and 

 North America; and in Climacium dendroides, also from Europe, the 

 operculum is lifted up in dry weather, but when the air is moist tLe columella 

 contracts again and closes up the mouth of the capsule. 



(h.) In the European genus Cinclidotus (fig. 2), which lives in water, the 

 columella is exserted and the filiform teeth of the peristome are twisted round 

 it, thus forming a cage as in Fontinalisy but on quite a different principle. 

 When the capsule gets dry or old the columella shrinks and breaks off the 

 upper part of the peristome, thus liberating those spores that had previously 

 failed to make their escape. 



In Splachnum (fig. 12) the columella is large, exserted, and dilated at the 

 top. In moist weather the teeth fold over the mouth of the capsule and touch 

 the dilated apex of the columella, but in dry weather they bend back until 

 they are adpressed against the outer side of the capsule. 



In our species of Dawsonia the filaments are, as I have said, free, but in 

 some Australian species these filaments, or cilia, are connected with the top of 

 the columella. In Wardia, from the Cape of Good Hope, the peristome 

 consists of an irregularly fissured membrane which adheres to the top of the 

 columella, and Scouleria, from North America, has thirty-two laciniated teeth 

 which are also connected with a process on the top of the columella, 

 (Berkely). 



But it is in the PolytrichacecE that the columella is put to the greatest use 

 for protecting the spores. In the genus Polytrichum (fig. 4) the top of the 

 columella is spread out into a thin flat drum-like membrane that extends over 

 the whole orifice of the capsule, and is connected at its edge with the mouth 

 of the capsule by thirty-two or sixty-four short processes formed of many 

 threads, like those in Dawsonia, soldered together, so that the spores can only 

 escape through the apertures between these processes, and consequently only a 

 few are likely to be blown out at a time. The genus Lyallia, from India, has 

 a similar membrane over the mouth of the capsule, bnt at length the columella 

 contracts within the capsule, and detaches a circular portion from the centre 

 of the drum, thus releasing those spores which have failed to make their 

 escape. As this membrane extends over the whole of the mouth of the 

 capsule, it entirely excludes the rain when the capsule is erect, which position 

 is therefore in this case better than an inclined one, and is that which nearly 

 every species of the family assumes. The species are equally distributed 

 between the plains and the mountains. 



