2o8 



The Journal of Heredity 



hybridizers did leave behind them 

 several legacies well worth while. 

 Kolreuter established the fact that 

 reciprocal crosses give very similar 

 results. A little later the efforts of 

 such men as Sageret, Wiegmann, 

 Gartner, and Naudin, placed three 

 other conclusions on a firm foundation 

 of experiment; the variability of hy- 

 brids of the second generation when 

 compared with those of the first, the 

 dominance of certain individual char- 

 acteristics, and the occasional reap- 

 pearance of the qualities lost to sight. 

 Possibly analogous observations had 

 been made previously by animal 

 breeders; but it is certainly within the 

 truth to say that even at the beginning 

 of the twentieth century these were not 

 accepted with anything like the unani- 

 mity which existed in the botanical 

 field. 



Morphology, with a much later 

 start, got down to essentials a great 

 deal more quickly than experimental 

 breeding. Indeed morphologists built 

 so rapidly during the Victorian era 

 they nearly reached a pinnacle of 

 success that would have given us a 

 different day to celebrate. They lacked 

 but the inspiration to put their "ifs" 

 to the test of calm experiment. 



THE CHROMOSOMES 



Logically it followed from the theory 

 of genetic continuity by cell division 

 that a material substance passed from 

 cell to cell is the basis of all heredity. 

 Naturally, then, the mechanics of cell 

 division was the subject of intense 

 investigation. The result was the 

 discovery that in building up the 

 tissues of the individual organism, in 

 the preparation of the reproductive 

 cells for their special work, and in the 

 behavior of these cells in carrying out 

 that work, there was an essential simi- 

 larity of the two processes in both 

 animals and plants. 



As these studies progressed it became 

 apparent that the cell nucleus was the 

 controlling agent of inheritance, and 

 that within the nucleus the chromo- 

 somes played the star role. This hy- 

 pothesis, put forth as a speculation by 



Haeckel in 1866, within fifteen years 

 gained the support of such eminent 

 investigators as Hertwig, Strasburger 

 and Van Beneden, largely because of 

 the similar elaborate preparations with- 

 in the nucleus of egg and of sperm 

 during maturation and of their ap- 

 parently dentical contribution of nu- 

 clear material in bi-parental inheri- 

 tance. Numerous investigations on 

 artificial fertilization were made by 

 adherents and opponents of this view; 

 but owing to the experimental difficul- 

 ties involved, they were not conclusive. 

 Polemic dissertations on the part 

 played by nucleus and cytoplasm fol- 

 lowed that were reminiscent of dis- 

 cussions in he realm of religion or of 

 politics. Gradually the proponents 

 of the view gained more and more 

 converts, not because they were able 

 to demonstrate a monopoly of directive 

 action by the nucleus in development 

 and heredity, not because they could 

 prove the intricate organization of so 

 many unfertilized eggs was controlled 

 by nuclear behavior, for such was not 

 the case: it came through small incre- 

 ments to cytological knowledge which- 

 gradually wove a mesh so fine that 

 there was no loophole of escape from 

 the conclusion. Belief in the impor- 

 tance of the chromosomes grew, as in 

 the case of organic evolution, not 

 because of direct proof, but because of 

 circumstantial evidence. Without go- 

 ing into an extended argument on the 

 subject, one may recall the constancy 

 of chromosome number in each species, 

 their individuality in size and shape, 

 the exactitude of their division during 

 growth, and their peculiar behavior at 

 the maturation of the germ cells. 



NINETEENTH CENTURY THEORIES 

 OF HEREDITY 



These facts, together with numerous 

 minor discoveries, were the basis of 

 nineteenth century theories of hered- 

 ity. But besides the efforts of the 

 practical breeders and of the morpholo- 

 gists, a serious attempt was made 

 by Francis Galton and Karl Pearson 

 to put genetic studies on a firm ground- 

 work of quantitative experiment. Es- 



