340 THE CELL 



viz. cells, so each cell is composed of numerous, small, hypothetical 

 elementary particles. 



Darwin, Spencer, Nageli, and de Vries have called these hypo- 

 thetical units by different names, although they mean the same 

 thing by them. Darwin (IX. 6) in his provisional hypothesis of 

 Pangenesis, calls them little germs or gemmulse ; Spencer (IX. 

 26), in his Principles of Biology, speaks of physiological units ; 

 Nageli (IX. 20), of particles of idioplasm or groups of micellae ; 

 and de Vries, in his essay upon Darwin's Pangenesis, calls them 

 Pangenas. 



What then are these small elementary portions of the cell, 

 which I will in future call idioblasts, in accordance with Nageli's 

 views, who, in my opinion, has most ably criticised the subject in 

 question ? 



It must be borne in mind, in answering this question, that no 

 precise definition of an idioblast can at present be given, like that 

 given by chemists and physicists of the terms atoms and mole- 

 cules. We are still on unknown ground, like the scientists of the 

 eighteenth century, who tried to prove that animal bodies were 

 constructed out of elementary units. Naturally, the danger of 

 going astray increases, the more we try to work this hypothesis 

 out in detail. I will, therefore, confine myself as far as possible 

 to the most general considerations. 



The hypothetical idioblasts are the smallest particles of 

 material into which the hereditary mass or idioplasm can be 

 divided, and of which great numbers and various kinds are 

 present in this idioplasm. 



They are, according to their different composition, the bearers 

 of different properties, and produce, by direct action, or by various 

 methods of co-operation, the countless morphological and physio- 

 logical phenomena, which we perceive in the organic w T orld. Me- 

 taphorically they can be compared to the letters of the alphabet, 

 which, though small in number, when combined form words, 

 which, in their turn, combine to form sentences ; or to sounds, 

 which produce endless harmonies by their periodic sequence and 

 simultaneous combinations. 



De Vries remarks that "just as physicists and chemists have 

 been obliged to resort to atoms and molecules, the biologist has been 

 forced to presuppose the existence of certain units, in order to ex- 

 plain by means of them the various vital phenomena." 



In Nageli's opinion, " the characteristics, organs, structures, and 



