216 THE MENDEL JOURNAL 



exist. In the case of the dog-whelk, very common around the 

 Enghsh coast, the differently coloured and banded varieties are 

 distinct, and though they have been seen breeding together, 

 nothing in the nature of blends or intermediates occur. 



It is therefore clear that the differences which distinguish 

 some forms from others are " discontinuous " and do not blend 

 in the hereditary transmission, but segregate. The question 

 which the future has to answer is no longer whether discontinuous 

 variations exist at all, nor is it any longer a matter of upholding 

 in an unquahfied fashion the contention that evolution is based 

 wholly on the blending and summation of continuous variations, 

 for the existence of discontinuous variations is now a fact. But 

 the question is one of whether evolution is wholly a matter of 

 discontinuous variations, or whether it is partly this and partly 

 due to continuous variations. 



All that can be said in the way of general considerations and 

 of essay speculations has already been written. The answer of 

 the future to these questions lies in experiment. No doubt, 

 observation of Nature has its value in suggesting new problems 

 and in controUing the interpretations of the experimental evidence. 

 But, by itself, it is insufficient to permit us to arrive at definite 

 and certain conclusions, which can be regarded as incontro- 

 vertible. 



Professor Bateson's book on " Mendel's Principles of Inherit- 

 ance " thus comes as the exposition of the experimental method 

 in biological science. In effect, he says : " We have done with 

 essay-writing, and the time is ripe for the apphcation of experi- 

 ment to all the problems of inheritance, variation, and evolution." 

 In the present book the author has preferred to restrict his treat- 

 ment of the subject to the concrete facts of inheritance, as they 

 have been ascertained by experiment. The consideration of the 

 theoretical conceptions which those facts suggest he has left to 

 be dealt with in another book. 



We may now glance, in a general way, at the contents of the 

 book and some of the problems with which it deals. In the intro- 

 ductory chapter there is an account of some pre-Mendelian 

 writings, and it includes Darwin's " Origin of Species," and 

 his " Animals and Plants Under Domestication," as well as those 

 of Francis Galton, Weismann, and some of the earlier works of 

 De Vries. The account of the pre-Mendelian writings is followed 

 by a statement of the way in which Mendel's paper was re- 

 discovered and of the new methods which he introduced into 

 the study of inheritance. There is also, in this chapter, a 

 description of the Mendelian principles illustrated by reference 

 to some recent experiments in breeding hybrids derived from a 

 cross between tall and dwarf sweet peas. 



