Varietäten, Descendenz, Hybriden, 195 



4. H. petiolaris Nuttall, 5. H. camis (Britton) Wooton and Standley, 

 6. H. argophylhts Torrey and Gray, 7. H. dehilis Nuttall, 8. H. prae- 

 cox Engelm. and Gray and 9. H. cucumerifolius Torrey and Gray. 

 Different varieties belonging to these species, are also mentioned. 

 The conclusions, reached at by the writer are as follows: 



1. The number of genes or determiners in Helimithus is not 

 infinitely great; it is probably very much less than exists in most 

 animals, and the study of the processes of heredity is relatively 

 simple. 



2. In the history of the sunflowers of the H. annuiis group, 

 there have been few really new developments. Species which seem 

 very distinct prove on exaniination to have few special characters 

 of their own. 



3. It is quite common for variations to arise, in wild and cul- 

 tivated plants, which appear to break the type, and initiate some- 

 thing altogether new. When, however, we begin to gather data on the 

 Variation of the Compositae, we find that practicaliy all these „new" 

 variations respect themselves in various species, and at various 

 times, indicating that they represent deep seated common tenden- 

 cies. Their occurrence among wild plants shows that they are not 

 necessarily connected in any way with cultivation, and it is equally 

 evident that they need not indicate any sort of hybridization, For 

 example, Ratihida coliimnifera presents many variations parallel 

 with those of Helianthus, in localities where it is the only species 

 of its genus. 



4. We are led, then, to think of the annual sunflowers as plants 

 representing a certain complex of potentialities or genes (of which 

 we may hope at length to make a reasonably complete catalogue) , 

 offering these in different combinations at different times, usually 

 failing to register any permanent advance, but once in a long while 

 reaching a new position of stability, suited to a particular environ- 

 ment. These positions of stability represent what we call a species. 



The perennial sunflowers appear to offer a more complex pro- 

 blem. Hundreds of what are considered „elementary species" are 

 found by S. Alexander in Michigan. The writer thinks to have 

 sufficient proof that all sorts of new combinations of characters may 

 arise within a type, without hybridization. 



Undoubtedly new determiners are formed from time to time, 

 but the occurrence must be so rare and so difiicult to demonstrate 

 that we can hardly hope to obtain satisfactory evidence concerning it. 



M. J. Sirks (Bunnik). 



East, E. M., The chromosome view of heredity and its 

 meaning to plant breeders. (American Naturalist. IL. p 457— 

 494. 1915.) 



The paper, based upon two lectures, delivered at Harvard 

 University, discusses at first the relative importance of nucleus and 

 cytoplasm, the morphological individuality of the chromosomes, the 

 physiological individuality of the chromosomes and the relations 

 between chromosomes and mendelian inheritance. The writer accepts 

 as a reasonable premise that the chromosomes are the chief if not 

 the sole bearers of hereditary determinants of body characters and 

 asks than, if there may be any cytological data, that can be made 

 useful at present or in the future to plant and animal breeders? 

 The discussion of this question is divided into three parts: 1. What 



