INTRODUCTION 



19 



there being any ' higher units ' in the germ as a superfluous one. 

 I can only explain this inconsistency by supposing that he re- 

 gards the ' quahties ' as independent and perfectly freely niisci- 

 ble, and, in fact, postulates a germ-mechanism which admits of 

 their separation in any manner required. If this were really the 

 case, and the primary constituents were not combined into fixed 

 groups in the germ, how could composite characters composed 

 of many different kinds of cells wuth a definite arrangement, — 

 e.g., the eye-like spot on a certain feather of a bird, — become a 

 fixed specific character? I am of opinion that the view which 

 entails an independence and uncontrolled miscibility of the qual- 

 ities is a fallacy, originating in the conception of amphigonic 

 reproduction as a necessary element in heredity. The chapters 

 on amphigonic heredity, reversion, &c., will show how I imagine 

 the idea of the uncontrolled miscibility of the separate qualities 

 to have arisen. 



It will frequentl}- be apparent in the course of this book that 

 my point of view is identical with that of the Dutch botanist in 

 many of the most important particulars. I believe, however, 

 that his * pangenes ' or similar minute elements do not suffice 

 in themselves for the construction of a theory of heredity, but 

 that something more must be added to make the phenomena 

 comprehensible at any rate in principle. 



The manuscript of the present book had already been written 

 for some time when Wiesner's work on the elementary structure 

 and growth of living substance * appeared. Although this mono- 

 graph does not contain, and is not intended to offer, a theory of 

 heredity, it is nevertheless of great importance in this respect, 

 for it treats of the fundamental points of such a theory, viz., 

 the composition of living matter out of ve>y small units. 

 Wiesner remarks that theories of heredity have hitherto always 

 adopted units invented for the purpose, whereas the same units 

 which make life possible at all, and which control assimilation 

 and growth, must also be the agents in bringing about the 

 phenomena of heredity. Spencer's ' physiological units,^ Dar- 

 win's ' gemmules,' HaeckeFs ' plastidules,' and my ' ancestral 

 germ-plasms," are all, in fact, elements of this kind, assumed 

 for the explanation of the problem of heredity. De Vries stands 



* y. Wiesner, ' Die Elementarstruktur und das Wachsthum der lehenden 

 Substanz,' W'ien, 1892. 



