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



characteristic member of the vegetation of the padi-fields is Pleurosigma 

 curvulum, Pritch., though rarely present in any great quantity ; another form 

 frequently found in small numbers is Fragilaria. I did not meet with 

 Pithophora or representatives of the Ulotrichales and Confervales in any of 

 the padi-fields examined.* 



The periodicity of the algal growth in the rice-fields would be an interesting 

 study, and would probably disclose interesting adaptations, which a brief 

 examination such as mine could not possibly reveal. It seems that the first 

 growth is almost always blue-green, and that the green element only appears 

 subsequently when the rice and occasional water-weeds (especially Characese) 

 afford a certain amount of protection against the strong light. Two fresh 

 rice-fields at Matale showed practically nothing but blue-green forms, whilst 

 a slightly more advanced field at Matara contained abundant Oscillaria inter- 

 mingled with occasional filaments of Spirogyra and Diatoms and Desmids in 

 some numbers. Old rice-fields often contained only very scanty Cyanophycese, 

 but in their place quite a rich Conjugate and Diatom flora. It almost seems 

 as though after the harvesting of the rice, and with approaching desiccation 

 the blue-green element again gains the upper hand, since dry padi-fields often 

 bear a filmy growth of some blue-green form on the stiff mud. I think the 

 sequence just sketched out is near the actual one, but there are certainly 

 occasional exceptions. 



I met with very few examples of marshy ground other than that afforded by 

 the padi-fields. Mr. Lewis kindly pointed out a fairly typical marsh to me 

 about two miles inland from Kalutara ; the ground was saturated with water 

 and covered by a rich growth of mosses with Urticularia, Nepenthes, etc. The 

 algal flora was that characteristic of such habitats in temperate regions, viz., 

 a very rich Conjugate flora with numerous diverse Desmids and a certain 

 number of Diatoms. Blue-green forms on the whole played a minor part. 

 A small extent of low-lying swampy ground about half-a-mile to the east of 

 Matara was covered by a rich growth of grasses, and was in most respects 

 unlike the marsh at Kalutara. The algal flora though rich in Zygnemacese 

 was exceedingly poor in Desmids, and Diatoms were common only as 

 epiphytes. There was a considerable growth of a narrow species of 

 (Edogonium at some points.f 



(iv) Algal Vegetation of the Bock-pools. — At diverse points (Nalande, 

 Dambulla, Kurunegala, Habarane) in the northern half of Ceylon one meets 



* It may once more be pointed out that the specific constitution of the green algal 

 flora is exactly the same as in the pools, ditches, and tanks (cf. p. 228 et seq). 



t One or two further (brackish) marshes will be considered in conjunction with the 

 estuarine flora in the second part of this paper. 



