relation between the periodicity of Microspora and the temp- 

 érature of the water, and that low températures are particularly 

 favourable to the development of the genus. A more or less 

 marked restriction of Microspora to the colder rnonths of 

 the year we liave also observed in other small ponds similar to 

 Barton's pond (1) . 



E. — The Confervales. 



The genus Conferva shows a rather similar periodicity to 

 Microspora, but exhibits a greater tendency to last into the 

 early summer. Thereare slight indications of two phases in the 

 annual cycle of tins genus, the one lasting from Mardi to June, 

 the other from October to December; this is seen in 1906 and to 

 a less extent in 1907 and 1908. 



It appears probable that the normal time for the increase to a 

 maximum in the case of Conferva is February or Mardi. This 

 was the case in 1906 and 1908 ; in both thèse years there was 

 nothing unusual in the amount of sunshine during the first three 

 months of the year. In 1907, however, the maximum of Con- 

 ferva was deferred till May; this corresponds to the occurrence 

 o.f an exceptionally sunny Mardi, wliich may hâve operated 

 adversely on the Conferva in one of two ways, viz. either by 

 favouring the development of the competing Oedogonium or by 

 exerting a direct deleterious influence on the Conferva itself. 

 Since the compétition of the Oedogonium, did not prevent the 

 development of Microspora {cf. p. 65), it seems probable that 

 Conferva was directly affected by the strong illumination. 

 There is a good deal of further évidence for such a view. Tlius, 

 in 1910 which also had rather a bright Mardi, the deve- 

 lopment of Conferva was again delayed till May. The decrease 

 of tlie genus after its maximum appears also invariably to 

 follow on unusual sunshine. Thus, in 1906 the decrease of 

 Conferva took place after an April with an exceptional amount 

 of sunshine; its abundance in May of 1907 corresponds to a rela- 

 tively low amount of sunshine for April and May of that year; 

 its decrease in July of 1908 follows on an exceptionally snnny 

 June; its relatively poor development in April and May of 1909 

 may be due to the large amount of sunshine in those months®. 



(1) e. g. in a pool at Edghaston near Birmingham, from which a séries of 

 samples was examineil in L903. 



(2) Itis difficult to interpret thisowingto the présence of the ducks. 



