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THE AMEBIC AN NATURALIST [Vol. LI 



Since not all the possible combinations of the 6 factors 

 have been tested, and 4 of the factors have not been tested 

 at all, either in combinations among themselves or with 

 any of the other 6 factors, the possibilities of linkage in 

 the tomato have only begun to be examined. It is note- 

 worthy that none of the 7 combinations which either do 

 or do not show linkage are at variance with the interpreta- 

 tion of linkage according to the chromosome hypothesis. 

 For instance, where one of two linked genes is unlinked 

 with a third, the other linked gene is also unlinked with 

 it. This is a necessity on the chromosome hypothesis.^ 



To fit the facts to the chromosome hypothesis it is only 

 necessary to assume that genes 1 and 7 are located in one 

 chromosome which we may call A ; genes 3 and 10 must be 

 located in another chromosome, B ; gene 4 must be located 

 in a third chromosome, C. Gene 8 can not be in A but 

 may be located in B, C or a fourth chromosome. With 

 these assumptions all the data so far obtained fall into 

 line and if these data are substantiated the other results 

 predicted must hold if the chromosome hypothesis is cor- 

 rect. It must be noted that many of the cases cited here 

 are not fully established on account of the small numbers, 

 and furthermore there is the possibility that what is taken 

 to be independent assortment may be crossing over of 

 about 50 per cent. 



be axiomatic and must hold for any and every hypotheses that might be put 



