238 Dr. F. E. Fritsch. On the Suba'erial and [Jan. 2, 



C. Leihleinii, Kiitz, and C. Jenneri, Ealfs) ; species of Euastrum (E. ansatum, 

 Ealfs ; E. obesum, Joshua ; E. dideltoides, West and West) ; and Netrium 

 digitus (Ehrenb.), Itzigs. and Kothe ; Cosmarium, Penium, Staurastrum 

 (more frequent in the uplands !) and Spirotcenia are of minor importance 

 and often scarcely represented. A number of filamentous Desmids* 

 {Gymnozyga moniliformis, Ehrenb. ; Hyalotheca dissiliens, Breb. ; Micrasterias 

 foliacea, Bail. ;f and more rarely species of Desmidium) are also characteristic 

 forms in these pools. Amongst the Diatoms, Pinnularia and various small 

 species of Navicula play the most important part, although only of occasional 

 occurrence. Pleurosigma and Surirella seem to be characteristic in some 

 cases, whilst, where water-weeds are present, Synedra lunaris, Ehrenb., 

 sometimes occurs as an epiphyte on them. The blue-green element is often 

 entirely wanting in these pools, and is never of any importance. 



Before proceeding to discuss the few data available regarding the biology 

 of this flora, it will be well to briefly sum up its constitution as follows : — 



(a) Dominant. — Species of (Edogonium and Spirogya, Pleurotamium 

 Trdbecula, P. annulatum, Closterium setaceum, C. pseudodiance, Triploceras 

 gracile, Netrium digitus. 



(b) Subsidiary. — Species of Bulbochcete, Euastrum, Pleurotamium, Closterium, 

 Cosmarium, Pinnularia, Navicula. 



(c) Occasional. — The remaining forms mentioned above and a considerable 

 number of others. 



Of all the forms enumerated, only Spirogya and (Edogonium are absolutely 

 constant, all the others being occasionally absent.^ Their absence may 

 be due to actual variations in this ferruginous flora, or to the pools 

 examined being in diverse phases, the latter, on the face of it, seeming 

 the more probable explanation. This brings us to consider the relation 

 between the algal flora and the characteristic granular deposit found in these 

 pieces of water. We are confronted by two possibilities. The flora may 

 have nothing to do with the deposit, or the latter may be due to the 

 activity of the Algas present. Such evidence as I have been able to obtain 

 points to the latter conclusion. Whenever there is a considerable growth of 



* Filamentous Desmids are, however, only a marked feature of the lowland pools ; they 

 are rarely present in those of the uplands (cf. p. 253). There is a very marked filamentous 

 tendency amongst these Desmids of the lowland pools ; this is exemplified by the presence 

 of a filamentous species of Micrasterias, a genus in which the individuals are usually single, 

 and by the frequent occurrence of short filaments of Triploceras gracile and Pleurotcenium 

 {e.g., P. annulatum). 



t This is the only species of Micrasterias I have as yet noticed in these pieces of water. 



% Pleurotcenium, Bulbochaite, Closterium setaceum, Triploceras, and the species of 

 Navicula are most widely present. 



