CLASSIFICATION AND NOMENCLATURE. 45 



1 1 7. Varieties. — Many forms differing only slightly from 

 the ordinary specific types, and yet capable of transmitting their 

 variations from generation to generation, are regarded as vari- 

 eties. It was the opinion of a prominent botanist, that all 

 so-called varieties among the lower plants " were purely the 

 result of the accident of environment, and never of cross-fertili- 

 zation." Since a species which varies in some minor particular 

 is likely to revert to the ordinary form as soon as the normal 

 conditions of soil, moisture, or environment are restored, there 

 is no scientific foundation for the multiplication of varieties to 

 serve as rubbish in works on systematic botany. A true variety 

 is an incipient species in process of formation ; when it becomes 

 sufficiently distinct to be regarded as a distinct thing with a 

 certain constancy of characters it is more logical to regard it 

 as a distinct species. In cases where species have been more 

 recently separated from each other in their evolutionary progress, 

 some intermediate forms may still persist. If the typical form 

 is clearly marked, these intermediate forms need not invalidate 

 its specific rank. 



1 18. Genera. — The limits of genera among ferns have given 

 rise to much difference of opinion. The few comprehensive and 

 heterogeneous genera recognized by Linnaeus were soon divided 

 by various authors, and other new genera were based on new dis- 

 coveries resulting from the exploration of newer portions of 

 the world. Adanson, Smith, Roth, Swartz, Bernhardi, Robert 

 Brown, and others added genus after genus, often passing over 

 the work of other post-Linnsean authors and often unwittingly 

 or even purposely renamed genera which had already well- 

 established names. Genera were largely based on the varying 

 arrangement of tlie sporangia on the veins, as well as the char- 

 acter, shape, and position of the indusia. The English of the 

 Hookerian school who have written on ferns have largely 

 depended on these characters and have tended to recognize 

 fewer genera than others of their countrymen or than are usu- 

 ally recognized by Continental botanists. 



1 19. Presl (1836) was one of the first to establish genera 

 based on the vascular systems of the plants, particularly their 

 methods of venation, and laid the foundation of a more logical 

 classification of ferns. John Smith, whose life had largely been 



