CHAP, in.] the Dogma of Constancy of Species. 113 



thus their true morphological character is often entirely 

 obscured ; on the other hand, the younger the organs are, the 

 less is this difficulty experienced, and this is the real reason 

 why the history of development is of so great service to mor- 

 phology. It was then one of the characteristic features of the 

 period we are describing, that its morphology was formed upon 

 the study of matured forms ; the history of development, or at 

 all events of very early stages of development, could not be 

 turned to account till after 1840, for skill in the use of the 

 microscope, here indispensable, was not sufficiently advanced 

 before that time to make it possible to follow the growth of 

 organs from their first beginnings. 



The establishment of natural affinities combined with the 

 assumption of the constancy of species, the growth of compara- 

 tive morphology without the history of development, lastly, the 

 very subordinate attention still paid to the Cryptogams, these 

 are the special characteristics of the period which has now to 

 be described at greater length. 



Here we must once more call attention to the fact, that 

 Linnaeus was the first to perceive that a system which was to 

 be the expression of natural affinities could not be attained in 

 the way pursued by Cesalpino and his immediate successors. 

 All who have attentively studied the writings of Linnaeus which 

 appeared after the ' Classes Plantarum' (1738) must have seen 

 the difference between that way and the one recommended by 

 him a difference which is the more obvious because Linnaeus 

 himself, like his predecessors, constructed an artificial system 

 on predetermined principles of classification, and always em- 

 ployed it for practical purposes, while he published at the same 

 time in the above-named work his fragment of a natural system, 

 and in the preface set forth the peculiar features of the natural 

 and artificial systems in striking contrast with one another. The 

 first thing and the last, he says in his prefatory remarks to his 



