230 Fertilisation and Hybridisation 



But we shall not yet leave the subject of the nuclei. 

 The independence of all the hidden potentialities, which 

 in the physiological field is most sharply defined in the 

 theory of pangenesis, we can of course not hope to see 

 reflected in the nuclei. We must, at least for the present, 

 be satisfied to find here any independent parts in the nu- 

 clei. 



It was well known to the older investigators, and, 

 among botanists, especially to Hofmeister, that the nuclei 

 are not structureless formations, but that they exhibit 

 more or less distinctly certain internal organs. But only 

 about a quarter of a century ago by means of better 

 methods of investigation did Flemming in the zoological 

 field, and Strasburger in the botanical, succeed in getting 

 a deeper insight into this structure, and soon afterwards 

 Roux showed how these achievements are entirely in har- 

 mony with the requirements of the theory of heredity. 

 Since then, numerous investigations have confirmed and 

 extended these results, and especially has Boveri brought 

 out the main features in the wide range of phenomena. 

 To him we owe the principle of the independence of the 

 individual visible component parts of the nuclei, a princi- 

 ple, which, in spite of much opposition, is more and more 

 strongly supported, and which has found in the most re- 

 cent studies of Sutton a brilliant confirmation. 



What Boveri's theory offers us is, in the main points, 

 as follows : All the bearers of hereditary characters lie in 

 the protoplasm of the nucleus, in the nuclear sap, as it is 

 usually called, as definite particles, which can be brought 

 out by various methods as distinctly recognizable parts, 

 and which are combined into threads. It is true that one 

 cannot see the individual bearers, because there are too 

 many of them and they are too small. Even a counting of 



