134 CLELAND 



structure and behavior, and this did not seem to have much bearing upon 

 the other branches of biology then in vogue. The identification and classifica- 

 tion of plants and animals did not seem to depend upon cellular phenomena. 

 Physiology was still concerned with the functions of organs and tissues and 

 had not reached down to the cellular level. Genetics was a science yet unborn, 

 and biochemistry was in its infancy. Cytologists did not need to master the 

 techniques of other sciences, nor were these sciences in turn concerned with 

 the findings of cytology. In only one direction was cytology a science which 

 involved more than one discipline. It was equally a botanical and a zoological 

 field. Plant and animal cytologists had much more in common than either of 

 them had with other branches of botany or zoology. And the fundamental 

 discoveries were equally shared by those working on plants and on animals. 

 Except for this one relationship, however, cytology remained a science apart 

 for some decades. 



The position of cytology changed, however, as it began to feel the need 

 for techniques from the other sciences to supplement its own and as other 

 sciences began to discover that the solution of their own problems required 

 going back to protoplasm itself, where alone the answers to the really funda- 

 mental questions are to be found. On the one hand, cytologists began to 

 utilize for their own purposes the techniques of genetics, biochemistry, and 

 histochemistry. On the other hand, they found themselves helping to furnish 

 the answers to the questions which the geneticists, the biochemists, the 

 taxonomists, and the evolutionists were raising. Cytology rather suddenly 

 became, therefore, an experimental, as well as an observational, science, and 

 it became a fundamental contributor to, if not an integral part of, other 

 important branches of biology. 



This transformation of the science of cytology began at the turn of the 

 century with the rediscovery of Mendel's work. This discovery marked the 

 birth of the science of genetics, and immediately this new science found a use 

 for cytology. Cytologists had been studying for some time the way in which 

 the cell and the nucleus within the cell divide and the behavior of the chromo- 

 somes, the sausage-shaped structures within the nucleus. They had been 

 speculating about the possible hereditary significance of the phenomena of 

 nuclear and cell division, of the peculiar cell divisions which occur at the 

 formation of reproductive cells, and of fertilization. When Mendel's work 

 was finally brought to light in 1900, cytological analyses had reached a point 

 where the parallelism between chromosome behavior and gene behavior 

 could be appreciated. It was Sutton (1903a, b) who was the first to make this 

 parallelism clear and to show convincingly that hereditary determiners are 

 distributed among the chromosomes and carried by them. From this time 

 on, cytology became a handmaiden of genetics, and its importance to genetics 

 soon became so apparent that the two sciences became to a considerable 

 extent fused into the new synthetic science of cytogenetics. 



