— 65 — 



to tlic development of Microspora tlian the other summers. 

 Further A.pri] to July had uniform heavy rainfaH and abnorm- 

 ally lit (le sunshine (Hopkinson 1912, pp. 93-94). The uni- 

 form rainfall would bring a constant supply of fresh air into 

 the water of the pond, winch wouid tend to be retained owing 

 to the prevailing low températures. It is therefore probable 

 tliat the water in the pond was far better aerated during the 

 summer of 1 ( .»07 than is usually the case, and tins may hâve 

 favoured the development of Ù& .Microspora and possibly hâve 

 led to the maximum in July. Such an explanation does not 

 however apply to tlie maxima of Mardi 1907 and April 1910. 



We must however take into account anotlier factor, which 

 undoubtedly plays some part in determining the frequency of 

 Microspora in the pond, and that is the compétition with other 

 forais, notably Oedogonium and Conferva (cf. the chart on 

 p. 66, and pp. 62 and 69). Ail three gênera are attached 

 during the early stages of their devedopment, and. since in the 

 early months of theyear, there is relatively little Phanerogamic 

 growth in the pond, there will certainly be some compétition 

 on the substratum. The resuit of this compétition will dépend 

 probablv on the set of meteorological conditions favouring one 

 or other genus. Thus in 1908, in which the necessary strong 

 sunshine occurred late, Oedogonïmn only became important in 

 June and thus left the field open for Microspora (and Con- 

 ferva). In 1907, the large nurnber of hours of sunshine in 

 Mardi led to an abundant development of Oedogonium, but eut 

 out the Conferva {cf. p. 68), which is usually important at 

 tins time; in the absence of the usually competing Conferva 

 there was obviously enough room for the Microspora and 

 Oedogonium and botli attained abundance at the same time. 

 Subsequently (April, 1907) how r ever the Oedogonium appears 

 to bave become too strong for the Microspora (1) , which 

 retired into the background until both Oedogonium and Con- 

 ferva had passed their prime, when (in July) the Microspora 

 attained a second maximum, probably favoured by the peculiar 

 meteorological conditions above described. In 1906, Conferva 

 appears to hâve flourished at the expense of both Microspora 

 and Oedogonium, neither of which were at ail abundant in the 



(1) The Microspora may hâve suH'ored t'roni the exceptional warmtb of 

 Mardi, 1907. 



5 



