PHYSIOLOGY OF REPRODUCTION IN PLANTS. 253 



to as many as three to seven in a group — in short to con- 

 vert the hermaphrodite plant into a male one, at the 

 expense of the female organs. It would be interesting to 

 learn how far the spermatozoids are capable of function. 

 The converse conversion could not be made. 



No less interesting are the results with other forms. 

 Parthenogenetic spores were produced in Spirogyra by 

 plunging the conjugating threads into selected salt-solu- 

 tions at the critical moment when union of the zvQfotes was 

 first about to be accomplished ; both " male " and " female " 

 cells were thus converted in spores capable of germina- 

 tion. Similar artificial productions of parthenospores in 

 Ulotkrix, Chlainydoinonas, etc., were also accomplished. 



The inhibition of the zoospores in Gidogonhun by 

 light or by running water — this plant was so wonderfully 

 under control that the author could make it develop zoo- 

 spores or sexual organs at will by altering the conditions 

 in definite ways — the artificial regulation of the sexes in 

 Ulothrix, etc., as well as many other points must be passed 

 over here. 



Hydrodictyon affords one of the best examples of all for 

 showing how conditions rule the development of reproductive 

 organs. It practically amounts to this. In any cell of the 

 net, it is possible at any time to cause either asexual zoo- 

 spores or sexual gametes to be developed by varying the 

 conditions in definite ways. There are perhaps limits to 

 the size of the cells — they must not be smaller than about 

 0'03 mm. for gametes and 6'2 mm. for zoospores— but 

 at any time during their growth to a length of 10 mm., 

 external conditions will determine whether growth shall 

 continue, or the contents be converted into zoospores or 

 into gametes. Klebs expressly states that he knows no 

 other Alga which is so plastic in these respects, for every 

 vegetative cell is equally capable of forming, at any time, 

 either zoospores or gametes according to the conditions 

 imposed. The importance of these facts with respect to 

 any hypothesis of alternation of generations is obvious. 



Enough has been given to show that Klebs' book will 

 have to be reckoned with as one of the best attempts yet 



