526 BOTANY pakt ii 



ment with Monocotyledons in floral construction, anatomical structure, 

 and in morphological characters. On this account the Monocotyledons 

 will be placed after the Dicotyledons in the following systematic 

 arrangement. 



Any direct transition from Gymnosperms to Monocotyledons is 

 thus out of the question while a relation of dicotyledonous plants to 

 Gymnosperms is not excluded. The best solution of this problem at 

 present is that of V^ON Wettstein who derives the simplest angiospermic 

 flowers from a gymnospermous inflorescence. If the systematic arrange- 

 ment of the Dicotyledons is based on this idea the most simply constructed 

 flowers would be those with one whorl of perianth segments and borne in 

 catkins. This assumption is supported by developmental evidence. 

 Thus the Casuarinaceae, Juglandaceae, Betulaceae, Ulmaceae, etc., will 

 be placed at the beginning of the system, and to them will be connected 

 the other families with a simple perianth which are grouped together as 

 Monochlamydeae. To these in turn may be connected the Dialypetalae, 

 the flowers of which have both calyx and corolla. The forms with a 

 gamopetalous corolla are separated as the Sympetalae, and the other 

 Monochlamydeae and Dialypetalae contrasted with them as Chori- 

 petalae ; the forms without perianth are grouped with the Choripetalae. 

 Since within the Monochlamydeae various lines lead from forms with a 

 simple perianth to those with a pentacyclic structure, any arrange- 

 ment in a simple ascending series is impossible. Various parallel series 

 lead from simple to highly organised floral structure, and similarly 

 numerous parallel series are found in the Dialypetalae. Thus the 

 natural or phylogenetic relationships can only be exhibited in an 

 incomplete fashion in the following arrangement (^^'). 



Class I. Gymnospermae 



1. Cycadinae: Fam. Cycadaceae. 



2. Ginkgoinae : Fam. Ginkgoaceae. 



3. Coniferae : Fam. Taxaceae, Pinaceae. 



4. Ghictinae : Fam. Gnetaceae. 



Class II. Angiospepmae 



Sub-Class 1. Dicotylae 



Series 1. Choripetalae 



A. Monochlamydeae 



1. Vcrticillatae : Fam. Casuarinaceae. 



2. Juglandiflorae : Fam. Juglandaceae. Myricaceae. 



3. Querciflorae : Fam. Betulaceae. Cujiuli ferae. 



4. Saliciflorac : Fam. Salicaceae. 



5. Urticinae : Fam. Ulmaceae. Moraceae. Cannabinaceae. Urticaceae, 



6. Loranthijlorae : Fam. Santalaceae, Lorantliaceae, Balanophoraceae. 



