— 59 — 



March-April) than in 1908 (in this case in .lune). In 1906 sucli 

 maximum as was observable occurred in May and .Tune, while 

 in 1909 it fell into April and May and in 1910 inlo May. If we 

 tu ni to tlie meteorological data for an explanation, we obtain no 

 help iVom rainfall or température. On tlie other liand the sun- 

 shine data show a very marked relation to the occurrence of 

 Oedogonium. In every case the increase in the amount of tlie 

 genus coincides with or follows immediately upon an exceptional 

 amount of bright sunshine (1) . Thus, in 1906 the 226 hours of 

 sunshine in April were followed by a maximum in May and 

 June ; in 1907 the 206 hours of sunshine in Mardi caused a 

 maximum in that month ; in 1908 there was no exceptional 

 amount of sunshine till May and June, and the maximum of 

 Oedogonium was only attained in the latter month ; in 1909 

 the large amount of sunshine in April and May caused a maxi 

 mum in those months ; while in 1910 May was the fîrst 

 really bright month and in tins month the Oedogoniums 

 becaine abundant(c/.also thecharton p. 60). Onemightalmostsay 



Table to show the occurrence of Oedogonium in Bar ton' s 

 pond, 1006-1910 (2) . 



that it requires sunshine amounting to about 200 hours in the 

 month to bring the Oedogoniums to their maximum. It should 

 be noted that the large amounts of sunshine in the months men- 

 tioned above do not always (though tins is frequently the case) 

 correspond to températures higher than the average, so that it 



(1) Cf. Brown, 1908, p. 236. 



(2) Regarding the symhols, see footnote 1 on p. 54. An ' indicates abundant 

 zoospore-lbrmation, as sbown by the numerous young plants. 



