- 6â — 



It was probably tins concentration of the water that prevented 

 the maximum from being immediately attained. 



As a gênerai rule after the maximum is over, Oedogonium 

 remains uniformly scanty ; it was only in 1907 that an increase 

 was observed in August, and tins lasted right into November 

 of that year. April to July of 1907 were characterised by uni- 

 form heavy rainfall, relatively small amount of sunshine and 

 relatively low températures ; thèse factors may hâve produced 

 an unusual dilution of the water by July, leading to a récupé- 

 ration of the Oedogonium. 



There is one other factor in the pond that may hâve sonie- 

 thing to do in determining the relative frequency of Oedogo- 

 nium, namely the compétition of other forms. There is some 

 évidence of compétition with Microspora and Conferva, 

 which will be considered under thèse gênera (pp. 65 and 69). 

 On the other hand it does not appear that the Conjugates 

 seriously afi'ect the abundance of Oedogonium (1 , which 

 appears to thrive very well side by side with them. Tlms, 

 in 1906 and 1908 Oedogonium and the Zygnemaceae are simult- 

 aneously dominant, although in 1907 owing to the early appear- 

 ance of the former this was not the case. Nevertheless it is 

 noteworthy that in 1910, when Zygnemaceae were practically 

 absent, Oedogonium was more abundant than ever before. 



The genus Bulbochaete is représentée! only by a single species 

 and that occurs very scantily. Apart from 1908, in which year 

 it was observed from May to August, it only occurred in May 

 of 1907 and an isolated spécimen in July of 1909. In view of 

 thèse scanty data it is impossible to draw any conclusions 

 regarding the conditions determining its occurrence, but it may 

 be noticed that its relatively long présence in 1908 coincides 

 with a period of uniformly bright sunshine. 



D. — TlIE GENUS MlCROSPORA. 



Microspora was found in nearly every sample taken from 

 the pond and is therefore a very regular constituent of the llora. 

 It is most abundant during the cooler parts of the year and is 

 generally least represented during the autumn (August-Novem- 



(1) Cf. Copeland, 1909, p. 14. Inasnmch as the Zygnemaceae are not atta- 

 ched forms, it would lie difficult to understand how much compétition could 

 arise. 



