THE CLASSIFICATION OF PLANTS 2155 



Certain broad principles of agreement are observable in these classifica- 

 tions, but it is obvious that the attempt to classify the Pteridospermae 

 should not be pushed too far at present. 



THE GYMNOSPERMAE 



The early history of the classification of the Gymnospermae is closely 

 bound up with the Angiospermae, for although the class was recognized 

 as distinct by Robert Brown as early as 1827, floristic writers continued to 

 treat them as Dicotyledons even up to the last fifty years. We need only 

 consider the views regarding the separation of the groups within the 

 Gymnospermae as a whole. There is a considerable amount of agreement 

 regarding the various orders, which are mostly well defined. Only in the 

 relative rank assigned to the different groups and in the subdivision of the 

 orders is there much difference of opinion. 



In the first edition of the " Pflanzenfamilien " (1889), Eichler treated 

 the Gymnospermae as divided into: 



Engler, however, in the " Syllabus " to the " Pflanzenfamilien " in 

 19 1 2, raised these families to ordinal rank and this was adopted in the second 

 edition of the complete work, dated 1926, where Pilger used the following 

 classification: 



1. Cycadales [ 



(a) Cycadaceae 



2. Bennettitales 



(a) Bennettitaceae 



(b) Nilssoniaceae 



(c) Caytoniaceae 



3. Ginkgoales 



(a) Ginkgoaceae 



4. Cordaitales ( 



(a) Cordaitaceae 



(b) Pityaceae 



Seward in reviewing recent types in the fourth volume of his " Fossil 



