250 Dr. F. E. Fritsch. On the Subaerial and [Jan. 2 r 



tion shows this to be due to a collection of air at these points. Pressure on 

 the cover-glass breaks up this air into numerous small bubbles, which speedily 

 become dispelled into the surrounding water, and after this process the black 

 dot at the base of the pila has vanished. Perhaps we have here an air-bubble 

 which was originally clinging to the rock- surface and formed the base for a 

 growth of Hypheothrix, since some algal forms are occasionally to be found 

 attached to the surface-film of air-bubbles in the water.* 



In concluding the discussion of this subject, I should like to point out that, 

 blue-green Algae in particular are noted for the frequent occurrence of dense 

 collections of very diverse forms, which have been one of the most fruitful 

 sources of the establishment of cases of so-called polymorphism. Had the 

 observers who dealt with this subject attacked the physiological problems 

 involved in these close associations of individuals, far more good would have- 

 been done than in the proclamation of cases of polymorphism on superficial 

 data. For such collections of blue-green Algae are certainly nothing more 

 than highly interesting consortia. 



(v) Algce of Wells and Springs (i.e., aerated but standing water). — I was 

 only able to examine three examples of the algal growth in wells, but they 

 have proved very instructive. The material is derived from three different 

 localities (Nalande, Matale, and Ambalangodda), so it may be looked upon as 

 fairly typical for the island. The fundamental point about these pieces of 

 water is their good aeration. The water is generally at some considerable 

 depth below the top of the well and is consequently not exposed to a very 

 strong light, nor is its temperature probably in any way as high as in the 

 more exposed waters we have previously discussed. The substratum is stone 

 or wood work. The prevailing conditions are thus very marked and uniform 

 and produce a very typical algal flora. 



The predominant forms are species of Pithophora, which were present in all 

 three cases and in two of them absolutely dominated the algal flora. In two 

 of the three wells at least there was also a certain amount of other 

 Cladophoraceae (Cladophora, Bhizoclonium). Since the material was in all cases 

 sterile and often covered with epiphytes, the discrimination of Cladophora and 

 Pithophora was not easy; the large mass of the Cladophoraceae present, 

 however, showed the vegetative characters described by Wittrockf as 

 characteristic of Pithophora. In two of the wells there was a certain amount 

 of Spirogyra presenting the usual features, whilst blue-green forms (Lyngbya, 

 Oscillaria) are always present, sometimes in quantity. CEdogonium was only 



* Cf. also Fritsch, "The Structure and Development of the Young Plants in 

 CEdogonium? 'Annals of Botany,' vol. 16, No. XLIII, 1902, p. 473. 

 t Cf. Wittrock, in ' Nov. Act. Reg. Soc. Sc. Upsala,' Ser. 3, 1877, p. 4. 



