PHYSIOLOGY OF REPRODUCTION IN PLANTS. 251 



zoospores ; and then he tries their effects on the develop- 

 ment of the sexual organs. 



Some results have been referred to. The difficulties 

 with lieht are ereat, but he comes to the conclusion that 

 apart from the assimilation effects, light-rays have an 

 influence of their own in inhibiting the development of 

 zoospores. Within the wide range of temperature (3°-26"C) 

 at which Vmichei'ia will grow, the lower temperatures 

 (3''-8°C) stimulate, while higher ones inhibit zoospore- 

 formation. 



Some curious results are obtained with inorganic salts. 

 Plants growing actively in nutritive solutions of suitable 

 strength refuse to form zoospores, and even darkening 

 them — usually a most effective method — will not stimulate 

 to zoospore-formation until the solution is diluted below a 

 certain point. Removal to pure water, however, at once 

 causes them to develop zoospores, and especially if 

 darkened at the same time. It is curious that these effects 

 can be got with solutions of sodium chloride and other salts 

 not usually recrarded as nutritive. 



Yet this effect cannot be got by transference from sugar 

 solutions to water : though it can if the Alga; be trans- 

 ferred from air or water to the sugar solution. 



Camphor gave extraordinary results. After eleven 

 days in camphor-water, transference to water caused zoo- 

 spores to form : on adding camphor again, the process was 

 inhibited, and even darkening failed to bring them — yet 

 after four days in this inhibited state, removal to water 

 induced the formation of zoospores in twenty-four hours, 

 and the Alga went on developing them for a week or two : 

 a re-addition of camphor at once stopped it, but removal 

 to water at once stimulated again, and so on. 



An interesting discussion follows as to whether the 

 above were osmotic effects, and comparisons of the osmotic 

 equivalents convinced Klebs that the explanation is not to 

 be found here. Nor does the (slight) acidity or alkalinity 

 of the medium explain it, as experiments show. 



Oxygen is not necessary, and some surprising results 

 are obtained as to the small quantities of oxygen needed 



