No. 526] SHORTER ARTICLES AND DISCUSSIONS 633 



Finally, Rosenberg 25 has invaded this fascinating field and 

 studied the hybrid sundews exhaustively. The main results of 

 his observations are similar to those given above in the case of 

 the other workers. Rosenberg adopts the explanation of "Un- 

 vertriiglichkeit (ineompatibility) for the behavior of the chro- 

 mosomes — a view which Tischler, 20 who speaks from much ex- 

 perience in the cytology of hybrids, believes to be inadequate, for 

 the reason that, as Rosenberg as well as he himself shows, there 

 are a few cases where typical embryo-sacs are developed and 

 indeed the anhtfic of the young sporophyte may he found. "Die 

 gewohnlidie Sterilitlit nicht in einer rnvertraglichkeit der bei- 

 derelterlichen Chromosomen liegt." 27 



We are able to see. therefore, that sterility, as far as may be 

 judged from studies upon the germ cells which have been made 

 thus far, is a matter of the fundamental constitution of the 

 organism. It concerns the bearers of hereditary traits, the 

 chromosomes. All of the studies which have been made point to 

 the conclusion that whatever may be its nature, there is an 

 "incompatibility" existing between the chromosomes of indi- 

 viduals of different species or varieties. Tischler 's contention 

 seems to me to be ill-founded, for the cases where normal struc- 

 tures occur in the embryo-sacs of these hybrid plants are exceed- 

 ingly few, and when we consider the observations of other 

 workers upon plant material, and of the animal cytologists we 

 find abundant reason to believe that the exceptions mentioned by 

 Tischler may be better explained in another way. Moreover, 

 we know nothing of the constitution of the nuclei of the cells 

 of the young sporophytes, with respect to the mingling of 

 maternal and paternal chromosomes. It may be, indeed, as 

 Gates has suggested, that a condition of apogamy may obtain. 



Undoubtedly the next few years will see many points as yet 

 undetermined, brought into proper perspective and we shall be 

 able to give a more complete account of the rationale of sterility. 



Max Morse. 



28 Rosenberg, O., " Cytologische unci morphologische Studien an Drosera 

 longifolia by rotundifolia," K. Vetenskaps Alad. Handh, Bd. 43, Nr. II., 



"Tiaehler, G., Zeitschr. f. ind. Abstammungsl., Bd. 3, H. 3, 1910. 

 37 Tischler, I. c. 



