RELATIONS BETWEEN THE NUCLEUS AND CYTOPLASM A 57 



present day is without a nucleus, it still remains extremely probable that 

 no differentiation into nucleoplasm and cytoplasm had as yet taken place 

 in more primitive forms than now exist. 



The character of every form of vital activity is determined by the 

 protoplast as a whole, i.e. by the co-operation and correlation between the 

 nucleoplasm and cytoplasm, and it is the union of these entities which 

 determines all the special peculiarities of a given species. If it were 

 possible to cause an isolated nucleus or cytoplasm to continue its life and 

 growth, either of these would probably present us with a new organism 

 having very different characteristics from those of the original protoplast. 

 The theories of heredity set up by Darwin, Spencer, and Nageli, in which 

 a part is ascribed to both nucleoplasm and cytoplasm, are just as much in 

 accordance with our present knowledge as are the deductive theories 

 originated by de Vries and Weismann, which are based upon the unproved 

 axiom that it is the nucleus alone which transmits hereditary characters 

 to the offspring. 



It is not necessary to discuss here either these hypotheses or the 

 problems of variation and heredity which they are supposed to explain. 

 They have already been dealt with in general terms in connexion with the 

 ultimate structure of the protoplast (Sect. 5). No hypothesis is necessary 

 to support the logical conclusion that, whatever changes take place, cells 

 must always be present somewhere or other which retain in themselves 

 a miniature replica of the characteristics and properties of the entire 

 organism and a potential power of developing and impressing these 

 characteristics upon the products of division. We may denote the plasma 

 of such cells as idioplasm, keimplasm, hereditary or embryonic plasm or 

 substance ', without connecting a particular theory with any of these terms. 



Just as the cells of an embryonic tissue may develop in widely 

 different directions, and when adult commonly lose all or most of their 

 embryonic properties, so also may the embryonic plasma be modified or 

 changed in a variety of ways, or undergo constructive or adaptive modifica- 

 tions which cause it to lose its embryonic nature and reproductive powers 

 partly or entirely. Observations made on plants decisively negative 

 Weismann's theory of heredity, according to which the 'reproductive plasma' 

 concerned in heredity and the preservation of the species, and the ' somato- 

 plasm,' by which the life of the individual is maintained, remain always 

 distinct and separate from each other, even when present in the same 

 protoplast 2 . 



1 It may be left an open question as to whether cells capable of forming new tissues (cambium 

 cells, &c.), but not of forming new entire organisms, are not also to be regarded as embryonic cells. 



2 Further details in the works of O. Hertwig, Delage, &c. 



