ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 587 



regions, and to show that the apparent similarity of algal growth all 

 over the world is less than is generally supposed. His results form an 

 epitome of our present knowledge of the distribution of these forms in 

 the tropics. The subjects treated are as follows: the systematic com- 

 position of the sub-aerial algal flora of the tropics ; of the submerged 

 aquatic algal flora, of the green algal element in the fresh waters of the 

 tropics (Cladophoracea3, Siphonea^, Conf ervales, Ulotrichales, Zygnemacese, 

 Desmidete, CEdogoniacete) ; of the fresh-water Floridete. The principal 

 conclusions arrived at are as follows : That in the damp tropics there is 

 always an extensive sub-aerial algal covering. In Ceylon this growth 

 consists almost entirely of Cyanophycese, which probably are equally 

 predominant in the other tropics, being essentially a tropical group and 

 the descendants of primitive algal forms. The subaerial green algse are 

 poorly represented except in case of Trentepohlia. In the submerged 

 algal flora and plankton, the Cyanophycese form an important but not a 

 preponderant element. In the submerged flora the narrow filamentous 

 forms are much more abundant than the broad, a fact connected with 

 the small amount of dissolved oxygen in the water. Gladophora and 

 Rhizodonium are poorly represented, while PithopJiora is more abundant. 

 Vaucheria and Botrydium are very rare. The Confervales, except 

 Opiiiocytium, are not well represented, nor are the Ulotrichales. Spiro- 

 gyra and (Edogo7iium are abundant. The Desmidefe exhibit a marked 

 filamentous tendency. Fresh-water FloridesB appear to be not at all 

 uncommon. 



Sub-aerial and Fresh-water Algal Flora of Ceylon.* — F. E. 

 Fritsch publishes the results of some observations made by him on the 

 tropical algal flora of Ceylon, from an ecological and biological point of 

 view. He indicates some of the more important differences between the 

 sub-aerial and fresh-water algal vegetation occurring in the tropics and 

 that found in temperate regions, and he points out the essential varia- 

 tions in tropical vegetation under the influence of diverse external 

 ■ conditions. The author presents his facts under the following headings : 



A. Sub-aerial algje, i.e. those growing on trees, stones, walls, etc. 

 1. The lowland vegetation. 2. The upland vegetation. 



B. Algal vegetation of the inland fresh- waters. 1. Algje of the 

 tanks and other large inland masses of fresh- water. 2. Algffi of road- 

 side ditches and pools in the lowlands, i). Algte of marshes and padi- 

 fields. 4. Algae of rock-pools. 5. Alga3 of wells and springs. 6. Algae 

 of the small pools of the uplands. 



The sub-aerial algfe of the tropics nearly all belong to the Cyanophycese, 

 which group plays a far more important part in the tropics than they do 

 with us. They require plenty of moisture and a fairly high temperature, 

 both of which they obtain in the tropics, and on account of their strongly 

 developed mucilage investments they are able to withstand the altera- 

 tion of wet and dry periods which prevail. As regards the algae of the 

 tanks in Ceylon, it is found that there also the blue-green element very 

 frequently dominates the entire algal growth. Two new species of 

 Desmids are described, growing in pools. 



* 



Pioc. Roy. Soc, Series B, Ixxix. (1>J07) pp. 197-254 (figs.). 



