PROBLEMS OF MODERN SCIENCE 



new form ? With this question in mind, it may 

 be imagined that when, in 1905, the opportunity 

 came to attempt an answer, the work was taken up 

 with great vigour. The method was to examine by 

 cytological technique under high magnification 

 the structure of the dividing nuclei in the pollen- 

 forming cells of the various types. In the follow- 

 ing year the first results were announced, and 

 they included the finding of different numbers of 

 chromosomes i.e., a new structure of the nuclei 

 in certain forms. This most unexpected and 

 gratifying result led to a decade of active research, 

 in which various workers have taken part. During 

 this period the nuclear structure or chromosome 

 number of many of these new derivative varieties 

 or species was worked out ; and by this means 

 the various relationships which they bore to the 

 parent species were determined, and an explanation 

 was also found for a number of their hereditary 

 peculiarities. These were some of the results of 

 an intensive cytological study of this group of 

 forms during a period of ten years. 



In order to make plain the bearing of these 

 results on the general conception of mutation, it 

 will be necessary to sketch briefly some of the 

 developments of the last two decades in cytology 

 or the study of cell-structure. That organisms 

 are composed of innumerable cells, which are all 

 derived from the division of a single cell the 

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