PHYSIOLOGY OF REPRODUCTION IN PLANTS. 249 



asexual organs or to Bower. The results are not always 

 the same, however, in either case. At the outset, some 

 species respond to a given stimulus fairly readily : others 

 again show little or no response, and it seems as if much 

 yet remains to be done ere we can explain the specific 

 differences. 



One is struck with the apparent similarity between the 

 cases where Vaitchcria remains sterile in moving water, as 

 Klebs finds, and those of many flowering aquatics which 

 are also sterile in quick streams. Schenck,^ for example, 

 says species o{ Hippuris, Sagittaria, Alisnia, Jilucils, Lito- 

 rella, Elatine, Sparganiuni, Callitricke, Potaniogeton, etc., 

 remain sterile in moving water ; and Klebs found that, like 

 Vancheria, Ulothrix and CEdogonhun are both induced to 

 develop zoospores by remov^al from moving- water — which 

 inhibits the process — to still water. Even slowly running 

 water inhibits the formation of sexual orofans in CEdooo- 

 nhim, and Klebs quotes an experiment (p. 279) where a 

 culture which remained sterile from the loth of June to the 

 20th of July in the moving water of his aquarium, at once 

 -developed the sexual organs when removed to quiet water. 

 As to Vaticheria, he declares that species which remain 

 sterile for months in running water at once form the sexual 

 organs if transferred to still water. The discussion as to 

 possible factors of explanation is very interesting, but too 

 long to reproduce ; he cannot explain it in detail. Another 

 interesting point is the experimental proof that transpiration 

 into a relatively dry atmosphere is an essential condition for 

 the development of the conidia of Euroliuni ; and we have 

 convinced ourselves in the Cambridge Laboratory that 

 sexual organs or conidia can be produced by following the 

 directions ; and here again one is tempted to draw compari- 

 sons with the numerous cases where the on-comino- of a 

 dry atmosphere favours the flowering of higher plants, as 

 pointed out by many observers. Moebius," among others 

 has collected cases showing that dry air and a moist soil 



^ Biolog'ie der Wassergezviichse, p. 107, 1866. Cited by Mobius, p. 

 130, Beiirdge znr Lehre von der Fortpflauz. 



- Beiliage zur Lehre von der Fortpflanzung. 



