THE POSITION OF CYTOLOGY IN BIOLOGICAL SCIENCE 9 



by a reunion of the parts into a more efficient whole. As each field has 

 <'xtcnded, its borders have come into contact with those of other fields 

 from which it ac(iuires aid for its own further development. Indeed, 

 1he n^gions formerly separating the fields are often found to be the most 

 fertile of all. 



The most conspicuous and so far the most profitable of such alliances 

 is that between cytology and genetics. Although much of the founda- 

 tion for this union was laid bj^ nineteenth-century cytologists and students 

 of heredity, modern cytogenetics dates rather definitely from 1900 and 

 shortly thereafter, when Mendel's laws of inheritance were rediscovered 

 and shown to have a physical basis in the known behavior of chromosomes 

 through successive life cycles. The remarkable results of this alliance 

 will receive special consideration in later chapters. 



A second alliance now undergoing development is that between 

 cytolog\^ and taxonomy. It has been found that characters useful in 

 classification can often be recognized in the number and the form of the 

 chromosomes. Not only do the chromosomal data aid in the grouping 

 of the species and ^'arieties, but they often furnish strong suggestions as 

 to the manner in which certain taxonomic units have arisen during the 

 course of evolution. The bulk of such work has so far been done with 

 plants, although the method has proved useful with certain animal groups 

 also. 



The study of chromosomes in related plants has led to the discovery 

 that diiTerences in chromosome number and form sometimes show a 

 significant correlation with differences in geographical range or ecological 

 habitat. Here again workers in different fields — ecology, phj'-siology, 

 and cytology- — are discovering the need for further cooperative endeavor. 



vSince disease is primarily an abnormal activity in cells and tissues, 

 the close relation between cytology on the one hand and pathology and 

 medicine on the other should be obvious. One needs only to mention 

 the imruly growth of cancer cells or the effects of viruses on cell structure 

 and function to indicate the importance of cooperative studies on diseased 

 tissues. 



The major problems of biology are thus joint problems, and coopera- 

 tion is the modern wa}^ of solving them. The benefits of the various 

 alliances are manifold. Cytology itself has been furnished with new and 

 effective tools; it has become more experimental in nature; its findings 

 have taken on new meanings. The other allied fields have been furnished 

 by cytology with a better conception of the physical basis of the phenom- 

 ena observed within their borders. The workers in all fields have been 

 made more fully aware of their dependence upon one another and of their 

 ignorance of much that assumes new importance for them ; this all makes 

 for tolerance and humility. Cooperation may make o\n- individual 



