252 SCIENCE PROGRESS. 



even for growth ; darkened cultures go on producing zoo- 

 spores for weeks. 



I have already referred to the startling results obtained 

 with running and still water. 



As regards the sexual organs, affairs are very different. 

 In the first place bright light is necessary for their forma- 

 tion, and secondly, sugar increases the tendency to form 

 them. Cases are quoted where Varicheria was kept grow- 

 ing for four and a half years in salt-solutions absolutely 

 sterile : yet, at any time, removal of a portion to sugar- 

 solutions, and exposure to bright light, induced the forma- 

 tion of sexual organs in four to five days! 



It is not a simple question of nutrition, though the 

 sugar is evidently used to afford nutriment ; for if fed with 

 sugar in the dark no sexual organs are developed, while 

 they torm in the light whether carbon dioxide be excluded 

 or not. 



Further experiments convince Klebs there is a light- 

 effect over and above that of assimilation ; but that only 

 the inception of the sexual organs depends on light-action, 

 for once incepted they can be made to complete their 

 development in the dark— no new ones forming mean- 

 while. 



The conditions being known, it is easy at any time to 

 obtain pure growths of sterile Vauchcria, and with such 

 Klebs found by means of artificial lights the intensity and 

 quality necessary to induce the formation of sexual organs. 

 The experiments with coloured screens are not devoid of 

 ambiguity, but the rays at the violet end of the spectrum 

 seem necessary. 



It is impossible to give even a sketch of all the experi- 

 mental results, and I must conclude with a reference to the 

 marvellous control obtained over the development of the 

 male organs. ]\mchcria rcpcns normally produces one 

 oogonium and one antheridium side by side at intervals 

 along the filament : by raising the temperature, or by 

 diminishing the air-pressure, Klebs was able to force all the 

 young oogonia to grow out to vegetative branches, or to 

 suppress them altogether, and to increase the antheridia up 



