Gates, Tetraploid Mutants and Chromosome Mechanisms. |;i~ 



At any rate, the characters of yiyas cited by de Vries as anta- 

 gonistic to this view are seen to be readily explainable in harmony 

 with it. Whether the leaf-shape requires the assumption of an 

 additional correlated change, remains to be seen, but the case of 

 Pliascwn cuspictatuui shows that this is quite possible. 



In yiyas Sweden many of the characters are obviously different 

 from those of yigcts de Vries, but the parental race of Laman-h- 

 iana from which it arose was also different (see Nilsson, 1912), 

 and until the chromosome numbers of both these races are known 

 it is useless to discuss the exact status of this giant race, though 

 many of its characters are obviously a result of the giantism of 

 its cells. 



The Chromosomes of 0. yiyas hybrids. 



Without occupying too much space with unnecessary details, 

 I may be permitted to refer to a few of the facts, chiefly cyto- 

 logical. Miss Lutz (1912) has devoted much of her recent paper 

 to a discussion of the probable status of the triploid plants which 

 formed the basis of my paper on chromosome reduction in 0. lata 

 X yiyas (Gates, 1909 b). There must, unfortunately, remain some 

 doubt as to the exact male parentage of these plants, but I think 

 the facts on the whole certainly justify my treatment of them and 

 I shall continue to refer to them as O. lata X yiyas. By ingen- 

 iously bringing together quotations from several of my early cyto- 

 logical papers, regarding the foliage and bud characters of these 

 plants, Miss Lutz has made statements appear contradictory which 

 in reality are not so. In the early papers the descriptions were 

 naturally less detailed than now when our knowledge concerning 

 the various types is much more accurate. Furthermore, the papers 

 were meant to be cytological rather than systematic. But anyone 

 familiar with the characters of Lcunarckiana, lata and yiyas knows 

 that the leaves, for example, of all three resemble each other 

 in varying degrees, and it was obviously my purpose in the cyto- 

 logical papers mentioned, to refer merely to the general features 

 of comparison. Since then, the necessity for very detailed studies 

 of the external characters has become clear, and much of my time 

 for several years has been devoted to the correlation of the cyto- 

 logical features with the external characters, only fragments of the 

 results of which have yet been published. 



I have also made the cross lata X yiyas a number of times 

 since 1907, but only once with success until this season. In 1909 

 I made the cross Lamarckiana X yiyas, obtaining an F t of forty 

 plants which were all identical with Lamarckiana. The pollen 

 when examined contained only triangular grains. Two F 2 families 

 were grown in 1911 and one F 3 in 1912, all giving typical Lamarck- 

 iana. This experiment is referred to in a paper now in press. 



