216 Dr. F. E. Fritsch. On the Subaerial and [Jan. 2, 



are rather more frequent. Embankments are generally covered with a thin 

 slippery film of gelatinous forms (e.g., the whole embankment along one side- 

 of Lady Horton's walk at Nuwara Eliya), and only at a few points are 

 these overgrown by tangles or tufts. The Algae (JVostoc, Aphanocapsa,. 

 Gflozocapsa, etc) concerned in the formation of these gelatinous films are all 

 characterised by having very highly mucilaginous (almost diffluent) sheaths. 

 But it is amidst the thick growth of Mosses and Lichens on the trunks of 

 trees that these gelatinous Algae often attain their greatest development ; 

 both on the wooded slopes of Pedrotallagalla and in the jungle on the 

 Hakgalla rock the luxuriance of their development is remarkable. In most 

 cases the Mosses are the more important epiphytes, but here and there 

 gelatinous Algae vie with them, either covering whole portions of the trunk 

 like the exuded resin or latex of an injured tree or hanging down in long,, 

 jelly-like masses between the Mosses and Lichens.* Such growth would be 

 almost an impossibility on a bare trunk, whilst it easily obtains a foothold 

 and maintains its position amongst the growth of Mosses, etc. The rocks 

 occurring in these jungles are remarkably poor in algal growth, which is 

 probably due to the absence of forms with a type of growth suited to such a 

 substratum. An almost diffluent Nostoc is not well suited for attachment to 

 a smooth rock-surface in a rainy region, and such growth as does occur on 

 these rocks is tangledf or very rarely tufted. The preceding remarks 

 indicate one of the chief factors in the uplands, viz., the competition of the 

 Bryophytes, etc. ; bearing this in mind, we can understand the scarcity of 

 tufted and tangled growth on moss-covered substrata, for it must inevitably 

 become overgrown sooner or later by the prolific Bryophyte and Lichen 

 vegetation. 



There are thus very obvious differences between the subaerial Algae of the 

 lowlands and those of the uplands, but the exact factors leading to this 

 diversity are difficult to determine. As above indicated (p. 207, footnote), 

 gelatinous forms with semi-liquid, diffluent sheaths, do not get on successfully 

 in the lowlands, because they are probably too susceptible to desiccation. 

 In the part of the uplands studied, the relative humidity of the air is 

 considerably greater than in the lowlands, whilst the temperature is, of course, 

 lower, and these seem to be the chief factors determining the enormous 



* The most important of these gelatinous forms are species of Glosocapsa, Glceothece y 

 Aphanocapsa, Nostoc, and Stigonema. Glceocapsa sanguinea (Ag.), Kiitz, possessing charac- 

 teristic red-coloured sheaths, was particularly common on some of the tree-trunks at 

 higher altitudes. 



f In one or two cases I met with tangles associated with a film of air such as were 

 described for the lowlands on p. 208. They are, however, of rather rarer occurrence in the 

 uplands. 



