290 



PROCEEDINGS. 



Friday, May ]1th, 1883. — Conversational Meeting. 



The sixth and concluding demonstration of the series was given this even- 

 ing by Kobert Braithwaite, M.D., F.L.S ., on "The Structure of Mosses." 



In his opening remarks, Dr. Braithwaite observed that he had great 

 pleasure in acceding to the request of the Committee that he should give a 

 demonstration on the structure of mosses, inasmuch as it was at the sugges- 

 tion of the President that he had made his first essay on the subject ; and 

 further, that would probably be the last opportunity he would have of 

 speaking about these matters in public ; and he could now speak with the 

 additional experience he had gained by working at the subject for some 

 years past. 



The mosses, looked at in a broad sense, formed an enormous aggregate of 

 species, probably 10,000 in number, scattered over the whole earth, and 

 especially delighting in wastes, woods, water-courses, rocks, and such like 

 places, where there was always a large amount of moisture. They might 

 be defined as cellular leafy cryptogamous plants, having the fruit enclosed 

 in a calyptra, through which it bursts, and a capsule containing spores. 

 But under this term were comprised various branches, and naturally the 

 whole group fell into three great sub-classes. 

 First, Sjphaffnince, or Peat Mosses. 



The peat mosses contain a single genus Sphagnum, comprising 50 or 60 



species. It differs from all the other groups in the structure of the leaves, 



which have heteromorphous cells, or cells of two distinct forms. In most 



cases the large or hyaline cells contain spiral fibres, but that is not an 



essential condition. The leaf cells of the Sphagninae are of a sigmoid shape, 



and contain between their walls smaller cells which give the colour to the 



leaves. The larger cells contain spiral fibres, and usually holes or pores 



abound in the outer walls ; the smaller cells contain chlorophyl, which gives 



the colour of crimson, or brown, or green to the plant. The branches are 



given off in fascicles or bundles, and the bark has a highly developed 



structure — one, two, three, or four layers of vesicular cells, with pores 



between, which form a distinct cuticle or bark, differing in this respect from 



the other mosses. The fruit has the ordinary urn-shaped capsule, throwing 



off the lid, and a calyptra, but without any peristome. 



The second group is the He2)aticince, or Liver Mosses. 



These are also thallaceous in a few cases, and they differ from the true 



mosses in having leaves lobed, imbricated in two rows, and the fruit case 



usually divided into fonr valves, and the spores have spiral fibres round 



them. 



