i o Introduction. 



which makes the character;' but the very man, who first 

 distinctly recognised this difficulty in the natural system, 

 helped to increase it by his doctrine of the constancy of 

 species. This doctrine appears in Linnaeus in an unobtrusive 

 form, rather as resulting from daily experience and liable to be 

 modified by further investigation ; but it became with his 

 successors an article of faith, a dogma, which no botanist could 

 even doubt without losing his scientific reputation ; and thus 

 during more than a hundred years the belief, that every 

 organic form owes its existence to a separate act of creation 

 and is therefore absolutely distinct from all other forms, 

 subsisted side by side with the fact of experience, that 

 there is an intimate tie of relationship between these forms, 

 which can only be imperfectly indicated by definite marks. 

 Every systematist knew that this relationship was something 

 more than mere resemblance perceivable by the senses, while 

 thinking men saw the contradiction between the assumption of 

 an absolute difference of origin in species (for that is what is 

 meant by their constancy) and the fact of their affinity. 

 Linnaeus in his later years made some strange attempts to 

 explain away this contradiction ; his successors adopted a way 

 of their own ; various scholastic notions from the i6th century 

 still survived among the systematists, especially after Linnaeus 

 had assumed the lead among them, and it was thought that the 

 dogma of the constancy of species might find especially in 

 Plato's misinterpreted doctrine of ideas a philosophical justifi- 

 cation, which was the more acceptable because it harmonised 

 well with the tenets of the Church. If, as Elias Fries said 

 in 1835, there is ' quoddam supranaturale' in the natural system, 

 namely the affinity of organisms, so much the better for the 

 system ; in the opinion of the same writer each division of 

 the system expresses an idea ('singula sphaera (sectio) ideam 

 quandam exponit'), and all these ideas might easily be explained 

 in their ideal connection as representing the plan of creation. 

 If observation and theoretical considerations occasionally 



