of Heredity 7 



These large classes of exceptions to go no further- 

 indicate that, as we might in any case expect, the principle 

 is not of universal application, and will need various 

 modifications if it is to be extended to more complex cases 

 of inheritance of varietal characters. No more useful work 

 can be imagined than a systematic determination of the 

 precise " law of heredity " in numbers of particular cases. 



Until lately the work which Galton accomplished stood 

 almost alone in this field, but quite recently remarkable 

 additions to our knowledge of these questions have been 

 made. In the year 1900 Professor de Vries published 

 a brief account* of experiments which he has for several 

 years been carrying on, giving results of the highest value. 



The description is very short, and there are several 

 points as to which more precise information is necessary 

 both as to details of procedure and as to statement of 

 results. Nevertheless it is impossible to doubt that the 

 work as a whole constitutes a marked step forward, and 

 the full publication which is promised will be awaited with 

 great interest. 



The work relates to the course of heredity in cases 

 where definite varieties differing from each other in some 

 one definite character are crossed together. The cases are 

 all examples of discontinuous variation : that is to say, 

 cases in which actual intermediates between the parent 

 forms are not usually produced on crossing t. It is shown 

 that the subsequent posterity obtained by self-fertilising 

 these cross-breds or hybrids, or by breeding them with each 

 other, break up into the original parent forms according to 

 fixed numerical rule. 



* Comptes Rendus, March 26, 1900, and Ber. d. Deutsch. Bot. 

 Ges. xviii. 1900, p. 83. 



t This conception of discontinuity is of course pre-Mendelian. 



