CHAP, v.] the Influence of the Knowledge of Cryptogams. 195 



the normal or ascending metamorphosis has no scientific 

 meaning unless species are supposed to be variable. It ap- 

 peared moreover that if the Cryptogams are made the chief 

 subjects of investigation, as Nageli made them, the so-called 

 metamorphosis of the leaves is a phenomenon of secondary 

 importance, and only attains to its full importance in the 

 Phanerogams. If Schleiden, illogically from his point of view, 

 conceived of metamorphosis as the principle of development, 

 Nageli on the contrary scarcely employed the word. He 

 regarded the history of development as the law of growth of 

 the organs, and, in accordance with the theory of the constancy 

 of species, the law of growth of every species and every organ 

 was invariable in the same sense in which we apply the term 

 to natural laws in physics and chemistry. In a word, Nageli's 

 considerations on the ' present task of natural history ' in the 

 work above cited, are not only logically and entirely consistent 

 on the principles of the inductive method, but they are also 

 consistent where others have been misled by the theory of the 

 constancy of species into illogical conclusions. 



Nageli set himself in earnest to meet the demands of induc- 

 tive enquiry, such as he had himself described them. It will 

 be shown more in detail in the history of phytotomy, how he 

 satisfied these demands in his refutation of Schleiden's doctrine 

 of the cell, and in the establishment of his own, and at a later 

 time in the framing of his theory of molecular structure and of 

 the growth of organised bodies, and how he made these inves- 

 tigations true models of genuine inductive enquiry. Here we 

 are concerned only with what he effected in this way for mor- 

 phology and systematic botany. In this field of research he 

 introduced two innovations of the profoundest importance, 

 which affected both the aim and method of enquiry for some 

 years. He connected his own morphological investigations, as 

 far as possible, with the lower Cryptogams, extending them 

 afterwards to the higher Cryptogams and to the Phanerogams ; 

 that is, he proceeded from simple and plain facts to the more 

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