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



of Anabcena (sometimes also Lyngbya, mainly L. majuscula). Narrow 

 species of Oscillaria are often present in minor numbers, but this genus- 

 plays a very unimportant part here in comparison to the pieces of water 

 discussed in the previous sections. The absence of Tolypothrix is noteworthy. 

 The blue-green element, though abundant, thus shows a very monotonous- 

 constitution, which is in striking contrast to the great diversity displayed 

 by the green flora. This is very well developed in all the rock -pools not. 

 dominated by Cyanophyceae, and also shows some uniformity in so far as it 

 consists almost only of Conjugates and Protococcales. But, for the existence 

 of forms belonging to these two groups, conditions must often be eminently 

 suitable, for such pools have furnished a diversity of forms, which only 

 finds its parallel in the upland pools. Diatoms (Fragilaria, Navicula) are 

 rare — in fact often as good as absent (none in 11 of the pools), but 

 Peridiniacese are often quite common amongst the members of the Conjugate 

 vegetation. (Edogonium, if present at all, generally plays a very minor part 

 amongst the Conjugates, although it attained considerable development in 

 a pool at Kurunegala and one at Hanwella.* The species of this genus 

 found in the rock-pools have generally rather broader filaments than the 

 species inhabiting the waters previously discussed, although none of the 

 forms could really be called broad. This feature may be connected with 

 better aeration. 



The abundant Conjugate element comprises certain species of Zygnemaceas 

 and Desmidiaceas, and although these forms have been shown to play a 

 part in the minor waters of the lowlands generally, we shall find that they 

 exhibit a markedly different aspect in the rock-pools. In the first place 

 Spirogyra is mostly only a subsidiary form, in many cases, indeed, of isolated 

 occurrence ; only in three of the 18 typical pools examined did it play an 

 at all important part, whilst in nine of them it was completely absent 

 (even in some cases in which the other Conjugates nourished). Two of the 

 three cases of abundant occurrence of Spirogyra are from the deep pools at 

 Dambulla, and this lends support to the view above suggested of the 



* The relative scarcity of species of (Edogonium in the rock-pools may have something to 

 do with the absence of a suitable substratum. The young plants tend to be epiphytes on 

 other filamentous Algae or on water-weeds ; the only filamentous forms present are 

 Conjugates, and these are well known to apparently afford an unsuitable substratum for 

 epiphytes, whilst water-weeds are rarely present. In the pool at Hanwella the 

 CEdogonium (0. calcareum ?) was attached to the rocky base, but this is the only example 

 of the kind noticed. At Kurunegala there was a little of a water- weed growing in the 

 rock-pool, and this bore the (Edogonium in this case ; in another rook-pool at the same 

 place many of the decomposing plant-portions forming a sediment at its bottom bore a 

 fair number of 2- or 3-celled young plants of the genus in question. 



