— 71 — 



[i thus appears thaï thelackof bright sunshine in the sum- 

 mer of n)<>7 was responsible for the relative importance of 

 Ophiocytium (1) . Attention should however be drawn to the 

 Fad thaï both July and August were colder in 1907 than usual. 

 Température mighl also account for the raritv of the genus 

 Iïoiii July onwards in 1906 and for the decrease in July of 1908. 

 Sunsliine liowever seems to bo tlie more important factor. 



On the whole therefore there is quite a considérable amount 

 of évidence to show that the two gênera of Confervales preseni 

 in the pond are influenced in their occurrence by the amount of 

 sunlight, altliough one cannot doubt that other not yet recog- 

 nised factors corne into play. The relation to sunlighl is 

 however différent from that of Oedogonium, which is brought 

 to its maximum by bright sunshine, whereas the forms under 

 considération are adversely affected (cf. also the chart on p. 60). 

 The large quantity of xanthophyll présent in the chloroplasts of 

 the Confervales raay be related in some way or other to 

 the light-sensitiveness of the members of this group ' 2 '. 



F. — The genus Chaetophora. 



As alreadv mentioned in the gênerai considération of the 

 annual cycle Chaetophora in Barton's pond is a well-defined 

 spring-form {cf. also Fritsch, 1903, p. 277, and Brown, 1908, 

 p. 229), being rare or absent at ail other times of theyear. Its 

 représentation is however a little varied and renders a brief dis- 

 cussion advisable. 



Itwill be seen that Chaetophora always attained its maxi- 

 mum in April, but whereas it was rallier common in 1907 and 

 1908, it was rare or at least rallier rare in the other three years. 

 In this connexion it may be noticed that the rainfall during the 

 early months of 1907 and 1908 showed no very pronounced 



(1) Both for the c&se of Ophiocytium and Conferva it may lie argued that the 

 light in summer is always much stronger than in winter, and tîiat therefore il 

 strong light in spring leads to a decrease of thèse gênera, they could not he 

 expected to stand any type of summer-illumination. It must liowever he 

 rememhered tliat in summer the Phanerogamous aquatics constitute a powerfid 

 screen to the Algae {cf. p. 36), and that therefore if the number of hours of 

 sunshine is helow the average the light may not hâve a ^reater effect than 

 spring-light. 



(2) The sensitiveness to sunlight may account for the relatively poor repré- 

 sentation of the group in the tropics {cf. Fritsch, 1907, p. 255). 



