264 PLANT PHYSIOLOGY 



are, therefore, inclined to believe that its reproduction and 

 its reproductive processes may also be similarly affected. 

 Yet this belief is so modern as to be almost heretical. The 

 morphology of reproduction has been studied by many; 

 very few have engaged in experimental studies of the phys- 

 iology of reproduction among plants. Of these few Sachs, 

 Vochting, and Klebs merit first mention. These men have 

 shown that upon external influences quite as much as upon 

 so-called inherited impulses depend the various kinds and 

 stages of reproduction. 



Klebs* studied certain algae and fungi in order to de- 

 termine the conditions under which they reproduce them- 

 selves. By experiment in culture he found that when cer- 

 tain conditions prevail, Vaucheria will form zoospores, 

 under other influences it will develop sexual organs and 

 reproduce itself through them. These conditions are repre- 

 sented in tabular form thus : 



VAUCHERIA SESSILIS f 



ZOOSPORES SEXUAL ORGANS 



Darkness after sufficient illumina- Light absolutely necessary for the 

 tion for adequate food-manufacture formation of sex-organs. Light suf- 

 invariably induces zoospore forma- ficient for healthy growth may be 

 tion. This will continue in darkness insufficient for formation of sex- 

 till there is no longer enough food, organs. Strong light needed, 

 though there may still be enough Light, apart from its effect on 

 for slow growth. nutrition, is a direct stimulus to 



form sex-organs. 



The addition of water to a culture Sex-organs form either in damp 

 in damp air induces active zoospore air or in water ; better in the for- 

 formation. mer. 



Temperature of 3 C. inhibits zoo- Same for sex-organs, 

 spore formation in all but accli- 

 mated forms. 



* Klebs, G. Die Bedingungen der Fortpflanzung bei einigen Algen und 

 Pilzen. Jena. 1896. The literature is here cited. A second volume, treat- 

 ing of the general questions of the physiology of reproduction in low or- 

 ganisms, is promised, but not yet published (1902). See also Jahrb. f. 

 wiss. Bot., Bd. 32, 33, 35. Falck, R. Die Bedingungen und die Bedeutung der 

 Zygotenbildung bei Sporodinia grandis. Beitrage z. Biol. d. Pflanzen, Bd. 

 VIII, 1901. 



f Klebs divides this species into three. The names of these, and the 

 reasons for division, not being essential in this connection, I retain the 

 old name. 



