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sions are thus confirmed by direct observation in nature. 

 Tliere is also évidence that unusuai concentration of tlie water 

 inhibits sexual reproduction in many forms. 



XXII. — In most cases sexual reproduction begins as soon as 

 tlie maximum is attained, but tliis is not invariable tlie case. 

 Many forms (but no t ail) die off almost completely al'ter sexual 

 reproduction is over. 



XXIII. — The rival views that sexual reproduction is 

 chiefly due to inhérent tendency and chiefly infiuenced by out- 

 side conditions are discussed at some length. On the basis of 

 tlie available évidence it is conciuded that the sexual process is 

 mainly deiermined by outside factors. 



XXIV. — The causes that lead to subséquent germination of 

 the spores of Algae are sought chiefly in external conditions, 

 although it is thought that inhérent tendency may inthiscase 

 corne into play to some extent. 



XXV. — Many species do not produce any marked resting- 

 stage in such a pond as Barton's, and it must consequentlv lie 

 conciuded that a few individuals uhvaysmanage topersistduring 

 the minimum period. 



XXVI — The présence of ducks during one year of our 

 observations exerted a very marked effect on the algal flora, the 

 filamentous forms in particular being very poorly represented. 



XXVII. — Oedogonium multisporum, Wood bas been 

 observed for the first time in tïiis country. 



East London Collège. 

 Àpril 12 th , 1D13. 



