MODERN BIOLOGY 557 



nevertheless afterwards survived; de Vries especially inherited it through 

 his theory of mutation, but, above all, Nageli's idioplasma theory was an 

 idea that was utilized by subsequent investigators with much profit. Here, 

 again, he really only invented a word, but the idea of a special substance's 

 being the bearer of the cell's hereditary qualities received remarkable con- 

 firmation in the above-described discovery of the role played by chromatin 

 in cell-division and its importance for the vital processes of the cell in gen- 

 eral. What prevented Nageli himself from drawing from his speculation 

 conclusions of practical value was undoubtedly his belief in ' ' absolute ideas ' ' 

 and the derivation of facts from them — a belief that he never really suc- 

 ceeded in eradicating. Herein, too, we must obviously seek the cause of his 

 attitude towards Mendel, violently criticized at a later date. The latter had 

 reported to him the results of his epoch-making experiments and received 

 in reply an inquiry as to whether the formulas he had set up were not "em- 

 pirical rather than rational." In these words is clearly shown the weakness 

 of Nageli's abstract-speculative method: he could not grasp Mendel's incon- 

 trovertible results based on fact, since they did not agree with his own the- 

 ories, and the correspondence, which went on for some time, though in 

 courteous terms, produced no result. With all his weaknesses Nageli never- 

 theless stands out as one of the foremost biologists of his time, and his 

 ideas had an influence long after his death. 



Among Nageli's pupils the first that deserves mention is his fellow- 

 countryman, Simon Schwendener (1819-1919), for a long time an assistant 

 to his master and finally professor at Berlin. Of his works should be men- 

 tioned one entitled Dasmechanische Prin^ip im anatomischen Bau der M.onokotylen. 

 In this he describes the mechanical functions of the cells and tissue elements 

 and shows how the structure of the plant closely follows the general laws 

 of mechanics governing its sustaining power and strength. In doing so, how- 

 ever, he sometimes interprets the structure and functions of plants from 

 a too narrowly mechanical point of view. Thus, for instance, he sets up a 

 mechanical theory in regard to the position of the leaves, wherein he exam- 

 ines the above-mentioned idealistic spiral theory and finds that the leaves' 

 spiral position is caused by conditions of mechanical stress and is altered 

 if the stress alters. In spite of its one-sidedness, however, this work contrib- 

 uted in its own sphere towards overcoming the romantic belief in an idea's 

 being the cause of a natural phenomenon and substituting a mechanical ex- 

 planation. Schwendener's works in the sphere of lichenology, however, 

 caused a still greater sensation than the above investigation. Hitherto the 

 lichens had formed a class in the vegetable kingdom by the side of Algas 

 and Fungi. Schwendener now declared, as the result of a series of micro- 

 scopical investigations, that the lichens are really a kind of double organ- 

 isms, consisting of fungous hyphas, in which cells of Algas lie embedded 



