— 100 — 



In Klebs' classical investigations (Klebs, 189G, pp. 96, 234, 

 242, 259, 279, etc.) lie sliowed that one of the chief conditions 

 for tlie production of sexual organs is a supply of briglit light. 

 It was l'ound that if tlie Alga was placed in a 2-4 per cent solut- 

 ion of cane-sugar, production of sexual organs took place at a 

 lower light-intensity than in tlie absence of such organic food, 

 but in no case could light be dispensed with. Klebs concludes 

 from tins that tlie light lias two parts to play, oue directly 

 stimulative (tins part non-repiaceable), tlie other serving for 

 tlie production of tlie necessary organic substance (tins part 

 replaceable by cane-sugar). The relation between sunshine and 

 the sexual reproductive process in Barton's pond is suffîciently 

 plain, as will be seen from the following table : 



A little explanation is necessary in the case of the later montlis, 

 but in Marcli and April the figures speak for themselves.In May 

 and June the table, although quite compréhensible l'or 1907 and 

 1908, appears at first sight rather anomalous for 1906. It must 

 be noticed however that the rainfall in Mardi, April and May of 

 1900 is much lower than in the corresponding montlis of the 



(1) Unly sexual reproduction is taken into account. 



