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On the Characters of certain gi-oups of the Class Personataz. 

 By David Don, Esq., Libr. L. S., &c. Communicated 

 by the Author. 



A considerable time has elapsed since I first commenced the 

 study of the various orders composing this important class of 

 plants, and my attention having been again more recently di- 

 rected to the subject, I have thought that the observations which 

 I have made might not prove unacceptable to botanical readers. 



The very close relationship that subsists between the several 

 families and groups of this class renders the circumscription of 

 them extremely difficult, and, indeed, in one like the present, 

 exhibiting a series of natural affinities almost uninterrupted, we 

 can scarcely hope to make out an absolute definition of any of 

 them. Nevertheless, the division of a large class into smaller 

 groups affords greater facilities to their study, and is advanta- 

 geous in pointing out their peculiarities of structure, and the 

 degrees of development in the various organs. 



In order to render this communication more useful in a prac- 

 tical point of view, I shall proceed to treat of the several families 

 separately, and conclude by giving the technical characters of 

 each. 



SCROPHULABINEiE. 



I have had occasion elsewhere * to remark of the Rubiacea?, 

 that they appeared to constitute a grand central point of union 

 between many families of the monopetalous class ; an observation 

 which may be applied with equal justice to the family now under 

 consideration, from the great diversity of form found in it, and 

 from its partaking, both in habit and structure, of those orders 

 to whom it is more immediately allied : for example, the group 

 of Scrophulariea closely approximates them to Verbascinect and 

 Solanece ; the Gratiolea connects them with Lentibular'ut ; the 

 Antirrhineo? and Gerardieee w ith Chelonea, and Bignoniacea ; 

 the Calceolariea, with Gesneriacea, ; the JEuphrasiea with Rhi- 

 nanthacew ; and their affinity to Verbenacete is clearly established 

 through the Ruddlejea. The Verbascinea. approach so closely 

 to the first group as to be only distinguished by their symme- 

 trical flowers. The normal Solanea are distinguished by the 

 plaited aestivation of their corolla, mostly regular flowers, and 



* Linn. Trans. 17- p. 109. 



