GENERATION AND INHERITANCE 303 



has gradually been confirmed in numberless other cases, in verte- 

 brates and invertebrates. And time and again that which we have 

 already seen has been repeated. These discoveries of the embryo- 

 logists placed new problems before the botanist, which he imme- 

 diately seized and solved. In the sharper position of the question 

 which was now possible, phenomena were gradually observed in 

 the Phcenerogamia and Cryptogamia, which, although no tso easily 

 explained as in the animal kingdom, showed that, in the develop- 

 ment of the vegetable sexual products, a reduction process by nu- 

 clear divisions following close upon one another, also occurred. Even 

 in Infusoria and different sorts of lower unicellular organisms, cor- 

 responding processes have been observed. 



We have reached in the realm of the study of generation a position 

 which has been attained to the same degree in the study of very 

 few of the other complicated phenomena of life. We can unite many 

 facts in a few general laws which possess value for the entire or- 

 ganized world and for which we can use the expression "law" with 

 the same justification and in the same sense as physicists and chem- 

 ists in their determinations of law-abiding phenomena of lifeless 

 nature. In a few decennaries discoveries have been made, which, 

 supplementing each other, have been connected with each other, 

 and have deepened in an unsuspected way our knowledge of gener- 

 ation. 



And as the middle point of these discoveries there stands a well- 

 characterized substance, which is contained in a small amount in 

 the nucleus of every cell, and whose striking changes during cell- 

 division have drawn upon it the attention of biologists, the chroma- 

 tin. That this wonderful substance must have a great importance 

 in the life of the cell is hardly to be doubted after the foregoing 

 experiences. Let us attempt to penetrate somewhat deeper into 

 its importance. We are hereby brought back to the important pro- 

 blem of inheritance upon which I already touched in connection 

 with the demonstration of fertilization, but had retained for later 

 mention. If the egg- and sperm-cell conveys to the new being 

 the properties of the father and mother, how does it come about, 

 we may ask, that these share in the process to such an unequal 

 degree, as the egg gives to the new being one hundred or one thou- 

 sand times more substance than the insignificant spermatozoon? 

 Naegeli, in his book Concerning the Mechano- Physiologic Theory 

 of Generation, which is very rich in ideas, has attempted to answer 

 the question by theoretic discussion, by the view that the sexual 

 cells consist of different substances, which possess a different value 

 for the inheritance of parental characteristics. The important sort 

 he designates idioplasm. 



Idioplasm is a purely hypothetic conception, for Naegeli himself 



