12 



between them as exist in any given series of either of 

 them — that is to say, differences may be found between 

 different individuals of any series of European plants, 

 and similar differences may be found between the indi- 

 vidual specimens of any American series, so that differ- 

 ences between the two series are to be expected — but 

 the differences that do exist are merely individual and 

 superficial, such as are common to all species, especially in 

 the Botrychia, where scarcely two plants are ever exactly 

 alike. Nevertheless, in spite of geographical separation 

 and range, specimen plants of equal age and development 

 from similar environments are to be found plentifully 

 enough to corespond perfectly in their fundamental, and 

 even in their external general characters. 



We cannot expect to find in nature exact agreement 

 among plants, such as we look for in the physical world 

 where patterns are struck off by dies so that each indi- 

 vidual is an exact counterpart of the other, but only such 

 agreements and differences as differentiate naturally 

 through the untrammeled operation of the forces of na- 

 ture, and no intelligent naturalist will ever become so 

 thoroughly imbued with the teachings of the schools as 

 to lose sight altogether of this great truth. One of the 

 unwritten laws of nature is that of Diversity — call it 

 evolution if you will, for it is evolutionary in its char- 

 acter — but it is that which gives to all living forms their 

 individuality, their agreements and divergences, by which 

 we are enabled to classify them within appreciable limits 

 for purposes of study. This classification and arrange- 

 ment of forms into such groups as exhibit close relation- 

 ships, artificial as it unquestionably is, appears to be nec- 

 essary for a complete understanding of the constantly 

 varying whole. But the broader and more elastic the sec- 

 tions into which any system is divided are made, the 

 greater latitude given to the subordinate divisions, and 

 the more .flexible species and varieties are. the nearer we 

 get to a natural arrangement of the complex forms that 

 are to be found everywhere in nature. 



