HISTORICAL SKETCH 441 



versial literature. Interest in the subject was greatly accentuated by the 

 suggestion that the mode of chromosome reduction affords a key to 

 certain phenomena of heredity. 



Cjrtology and Heredity. — As Wilson (1900) points out, the many 

 facts brought to light in the early days of cytology were of the greatest 

 significance in connection with the theory of evolution and the problem 

 of heredity, though for many years this was only vaguely perceived. 

 Darwin, aside from his hypothesis of pangenesis, scarcely mentioned 

 the theories of the cell, and not until many years later was the cell 

 investigated with reference to these matters. Researches on the origin 

 of the germ-cells, nuclear division, and fertilization, which brought 

 cytological research and the study of evolution and heredity into inti- 

 mate association, began shortly after 1870 with the works of Schneider, 

 Auerbach, Fol, Btitschli, 0. Hertwig, C. Bernard, van Beneden, Stras- 

 burger, and Flemming. These were followed by the noteworthy achieve- 

 ments of Boveri, Driesch, Herbst, Morgan, Loeb, and others. These 

 men laid the foundations for the work which has followed, and their 

 researches, greatly aided by the development of new refinements in 

 microtechnique,^ ushered in modern cytology. 



A powerful stimulus to investigation w^as given when the zoologists 

 Hertwig, von Kolliker, and Weismann, and the botanist Strasburger, 

 concluded independently and almost simultaneously (1884-1885) that 

 the nucleus is the "vehicle of heredity," an idea which Haeckel had put 

 forward as a speculation in 1866. The announcement of this conception 

 led to an even more intensive study of the nucleus and of its role in hered- 

 ity, a study which is now in progress and which, more than any other 

 one thing, can be said to characterize the work of our modern period. 



Special mention should be made of the theory developed by August 

 Weismann (1834-1914), because the modern nuclear theory of heredity, 

 although resting on a substantial foundation of observational and 

 experimental evidence, is largely an outgrowth of his speculations. 

 It may be noted that Weismann incorporated in his theory several points 

 of earlier theories, particularly those of Darwin, de Vries, and Nageli.^ 

 His various hypotheses were set forth in his Das Keimplasma (1892) 

 and in more elaborated form in his Vortrdge iiher Deszendenztheorie (1902). 



Weismann identified the supposedly distinct inheritance material, or 

 germ-plasm (idioplasm), about which there had been much speculation, 

 with the chromatic substance of the nucleus. His conception of its 

 constitution was essentially as follows. The ultimate living unit is the 



6 For the history of staining, see Conn (1928a6, 1929, 1930a6, 1933), Conn et al. 

 (1929), Conn and Kornhauser (1928), Kornhauser (1930), and Conn and Cunningham 

 (1932). 



' For fuller treatments of this subject, see Kellogg (1907), Delage and Goldsmith 

 (1913), Thomson (1899, 1913), ConkUn (1915), and the second edition of this book. 



