197 



V. THE ALLIANCES OF PLANTS. 



THE following pages explain the author's own views of arrange- 

 ment in 1836, and serve as a key to the Natural System of 

 Botany (Edition 2, London 1836). Although his opinion is much 

 modified by subsequent consideration, yet he knows from expe- 

 rience that these short characters are of considerable value to 

 students. 



CLASSES. 



The whole vegetable kingdom is divisible into five principal classes, 

 which may be characterised as follows : 



/^Exogens with their seeds 

 \ in an ovary . I. EXOGEIXLE. 

 'having spiral/ Exogens with naked 



vessels J seeds . . II. GYMNOSPERMJE. 



VEndogens . . III. ENDOGEN^l. 

 without spiral vessels, or with scarcely 



any ..... IV. RHIZANTH^. 



Propagated without sexes .... V. ACROGEN^E. 



They are further known by a separate consideration of the nature of 

 all their principal organs, thus : 



Propagated 

 by sexes 



The five classes form a circle, the centre of whose circumference is occupied by Exogens 

 and Endogens, the common point by Acrogens, and the intermediate spaces by Gymno- 

 spermse and Rhizanthae, which are transition classes. This may be expressed thus : 



Exogens, Endogens, 



Gymnospennae, Rhizanthae, 



Acrogens. 



This proposition is to be demonstrated in the course of the following explanation of the 

 characters and affinities of the various Classes, Subclasses, Groups, Alliances, and Natural 

 Orders, of which the vegetable kingdom consists. 



