2IO 



The Journal of Heredity 



tween the determinants of the germ 

 cells, and for individual development 

 by a qualitative distribution of the 

 determinants of those cells set apart 

 to build up the bodies which were to 

 act as hostelries for the immortal 

 germplasm. 



With Weismann is reached the peak 

 of genetic generalization at the begin- 

 ning of the twentieth century. Today 

 we have parted company with him in 

 many particulars, nevertheless if mod- 

 ern genetic theory can be said to be the 

 outgrowth of any earlier school, the 

 Weismannian school must be given the 

 preference. As Wilson has said, he 

 brought "the cell theory and the evolu- 

 tion theory into organic connection." 

 His work, besides dispelling many old 

 wives' notions by its cutting logic, was 

 second only to that of Mendel in 

 making genetics an experimental 

 science. Morgan credits him with "the 

 basis of our present attempt to explain 

 heredity in terms of the cell" in that 

 he propounded three of the principles 

 upon which the modern Chromosome 

 Theory is founded. 



WEISMANN AND MENDEL 



Some may see an inconsistency in 

 ascribing the ground-work of current 

 ideas of heredity to Weismann, and 

 yet celebrating the rediscovery of 

 Mendel's papers as the true break be- 

 tween the old and the new. The 

 obvious reply would be that it takes 

 more than three foundation stones to 

 prop up a useful structure, and that 

 Mendel furnished several examples, 

 most beautifully cut and polished. But 

 there is a deeper truth than this to be 

 emphasized. Weismann unquestion- 

 ably had a breadth of mental vision far 

 exceeding that of Mendel. He was a 

 real clairvoyant of science, too, and not 

 a mere visionary in the cynical modern 

 sense of the word. Nor was he above 

 the drudgery of experiment. But he 

 failed to have the good luck of initiat- 

 ing a simple method whereby the 

 elementary quantitative relationship 

 between hereditary phenomena could 

 be tested and retested by those who 

 followed him. This fortune fell to 



Mendel, who, though in a comparative 

 sense a narrow man, was yet able to 

 grasp somewhat of the significance of 

 the results obtained, and leave an 

 imperishable monument to his name. 

 No one may say he was the greater 

 man, but no one can deny he left the 

 most useful work. His results are a 

 satisfaction to the rank and file of 

 scientists for just this reason. They 

 leave a ray of hope to the plodders 

 with whom most of us trail. 



The path opened up by Mendel has 

 joined with the path cleared by mor- 

 phology to produce a road that has 

 extended some distance during the 

 past two decades; but to point out the 

 cairns and avoid falling into the pits is 

 not an easy task. The roadmakers 

 have been numerous, and in general, 

 honestly constructive; but in order 

 to hold this article within reasonable 

 limits I shall mention few names except 

 to pay a just tribute to Morgan as the 

 master craftsman. Nor shall I speak 

 of the attempts at sabotage, except to 

 say they have become more and more 

 infrequent. I shall merely endeavor 

 to recapitulate the fundamental points 

 as best I may w'th the hope that the 

 effort will not be far afield. At the 

 risk of becoming wearisome I want to 

 try to estimate the progress in terms of 

 general conclusions rather than to 

 describe a heterogeneous selection of 

 ancient heredity puzzles that have 

 yielded to simple interpretations. 



GENETICS AND EVOLUTION 



First, it must be emphasized that 

 though modern genetics has brought 

 about a clearer orientation of the 

 problems of development and of evo- 

 lution, it has been concerned directly 

 with the mechanism of heredity. Least 

 progress has been made in connection 

 with the problems of ontogeny. But 

 the conception of where the one ends 

 and the other begins, in so far as this 

 is possible, has become much more 

 definite — at least in this country. It 

 is probable that the interesting phe- 

 nomena recently described by Mr. 

 Bateson where seeds from various 

 parts of the same plant apparently 



