56 THE AMERICAN B(3TANIST 



has by far the more satisfactory keys, but it is open to the 

 objection that it incHnes to make species of every slight dif- 

 ference and the nomenclature employed is one that is dis- 

 credited by the rest of the world. Gray's manual is much 

 more conservative as to the species and uses the standard 

 nomenclature, but the keys are often very unsatisfactory, be- 

 ing perhaps scattered through the text, or divided into many 

 different sections, any one of which may lead the unwary 

 astray. In Gray's book too, the distinguishing character- 

 istics are italicised in the text, while in Britton's such charac- 

 ters are found in the key. In general one finds that first one 

 key and then the other is more useful and in many cases one 

 book may supplement the other. It might be asked why we 

 should use such keys at all, since the popular handbooks have 

 artificial keys which often trace the species with less labor. 

 The reply, of course, is tliat the popular handbooks contain 

 only the more showy species and when we are investigating 

 little known plants or closely resembling species, a more exact 

 set of descriptions are needed. So one might as well learn to 

 use the technical keys in the first place. 



The general framework of the natural system for identi- 

 fying plants is very easily understood. The entire plant 

 world is first divided into a number of groups and these are 

 then subdivided according to relationship which is, of course, 

 according to the descent. All those in a single group may 

 be assumed to have had a common ancestor and naturally re- 

 semble one another more than they resemble those of other 

 groups. A common method of making the first division is 

 to make four groups. These in the order of their complexity 

 are the Thallophytes (algae and fungi), the Bryophytes 

 (mosses and liverworts), the Pteridophyt£S (ferns and their 

 allies), and the Spermatophytes (seed-bearing plants). Mod- 



