INTRODUCTORY. 217 



the natural system cannot be regarded as being perfectly evolved ; 

 the various general sketches which have hitherto been given are 

 therefore no more than approximations to the truth. The system 

 followed in the following pages has no pretension to be regarded 

 as absolutely correct ; it is simply the arrangement which appears 

 to answer most nearly to the present state of knowledge of mor- 

 phology and affinity. 



The following are the main divisions of the Vegetable King- 

 dom : 

 IST GROUP. Thallophyta. 



Class 1. Algae. 



Class 2. Fungi. 

 2ND GROUP. Bryophyta. 



Class 3. Hepaticag. 



Class 4. Musci. 

 SRD GROUP. Pteridophyta. 



Class 5. Filicinae. 



Class 6. Equisetinae. 



Class 7. Lycopodiiise. 

 4TH GROUP. Phanerogamia. 



Division A. Gymnospermce. 



Class 8. Gymnospermae. 

 Division B. Angiospermce. 



Class 9. Monocotyledones. 



Class 10. Dicotyledones. 



In considering the distinguishing characteristics of these four 

 great groups, it may be pointed out, in the first place, that whereas 

 in the Bryophyta, Pteridophyta, and Phanerogamia, without ex- 

 ception, the life-history presents a regular alternation of genera- 

 tions, in the Thallophyta the alternation is generally irregular and 

 is, in many cases, altogether wanting. The Thallophyta and the 

 Bryophyta agree with each other, and differ from the Pteridophyta 

 and the Phanerogamia, in that (a) in their life-history, "the 

 plant " that is, the form to which the name is attached (see p. 3) 

 is, generally speaking, the gametophyte, whereas in the two 

 latter groups it is the sporophyte ; and in (6) the relatively rudi- 

 mentary differentiation, both morphological and histological, of 

 their sporophyte, whereas their garaetophyte is commonly more 

 highly differentiated than that of the two latter groups. Finally, 

 though resembling them in. many respects, the Phanerogamia differ 

 from the Pteridophyta in that they produce seeds : in fact, the 



