1907.] Fresh-water Algal Flora of Ceylon. 213 



substrata are colonised as are suitable for their development. Tree trunks 

 and smooth rock-surfaces, even in very wet localities, are often only provided 

 with a very poor algal covering, since the hard bark or rock is suitable only 

 for adhesive growth ; the latter, however, probably meets with considerable 

 obstacles in the way of establishing itself owing to the very heavy downpours 

 of rain which scour the surface of the tree or rock. If these difficulties are 

 successfully overcome in early stages, adhesive growth may become 

 established, and will then, in course of time, prepare the way for other forms 

 of growth. Decayed trunks, of course, form a much more suitable sub- 

 stratum and generally bear rich algal growth of various kinds. In protected 

 -situations adhesive growth becomes well developed, especially on walls, 

 rocks, embankments, etc., and is almost invariably the forerunner of tangled 

 and tufted growth. In many cases it is quite possible to detect the remains 

 of an adhesive growth at the base of tangled or tufted growth (fig. 1, B, D) ; 

 mostly, however, such adhesive growth is quite dead. It appears more 

 commonly to consist of unicellular encrusting forms than of filamentous 

 species, and the former by their decay probably afford a kind of soil for 

 iurther colonisation. In the dry regions, adhesive growth is predominant 

 everywhere. Heavy downpours of rain probably make it impossible for 

 larger gelatinous forms to obtain a foothold except in very sheltered 

 -situations. Tangled growth, since it helps to bind the clay of an embank- 

 ment together, and to make it more suited to withstand a heavy downpour of 

 rain, is liable on such a substratum to be much more successful in exposed 

 situations than an adhesive growth ; and such embankments may furnish 

 *a foothold for tangled forms without any previous growth taking place, 

 although in many cases there is a passing preliminary growth of the adhesive 

 type. The tangles again give way to tufted growth, which generally gains 

 the upper hand ultimately. This tufted growth, as already mentioned above, 

 may belong to the same form as constitutes the basal tangle, or may be due 

 to a distinct tufted species. Thus Symploca is very commonly found growing 

 on a basal tangle of Tolypothrix, whilst in other places small Mosses are 

 found arising vertically from a similar base or even from a dense tufted 

 growth of one species or the other. In both cases I frequently found some 

 of the filaments of the basal tangle of Tolypothrix using the Symploca or the 

 Moss, as the case might be, as a kind of support round which they twined 

 themselves closely (fig. 2) ; they thus raise their filaments out into the air 

 and, in fact, form a kind of upright growth quite comparable to a tuft,* at 



* This, no doubt, also illustrates the mode of formation of a tuft. One or two out- 

 standing branches first arise from a tangle, and these serve as supports for further 

 branches which grow up round about them. 



