THE CLASSIFICATION OF PLANTS 2153 



or the other. In the Pteridospermae the production of seeds on the 

 fronds is the only definitive character and a great many fronds are known 

 which are suspected of belonging to the group but have not been found 

 in a fertile state. There are also a number of anatomically preserved 

 stems which show relationships to both the Pteridospermae and the 

 Cycadales and indeed may belong to an evolutionary sequence between 

 those two groups, but it is impossible to say where the line should be drawn 

 or whether these plants belonged, in fact, to either of the groups. The onlv 

 attempts at classification have been based chiefly on the seed characters and 

 cover therefore, with certainty, only those forms of which the seed structure 

 is known. Seward in his " Fossil Plants " remarks that the practice of 

 classifying fossil plants has been carried to excess. Some sort of grouping 

 is desirable as a matter of convenience no doubt, but it is very definitely 

 Alpha Taxonomy and should not be allowed to create a prejudice in the 

 mind in favour of a genetic relationship which may or may not exist. 

 Seward distinguished three classes of Pteridospermae: 



I. Lyginopterideae 

 II. Medulloseae 

 IIA. Steloxyleae 



LTnder these headings are grouped a variety of organs; stems, roots, leaves, 

 seeds, etc., which are believed to be related. This classification, however, 

 can be crossed by another, applying to the seeds only: 



1. Lagenostomales (seeds belonging to members of the Lyginopte- 



rideae). 



2. Trigonocarpales (seeds belonging to members of the Medulloseae). 



3. Cardiocarpales (Gymnospermic seeds probably belonging to Cor- 



daitales). 



The stem material, showing anatomical characters which are related to 

 Pteridospermae, but with certain cycadean features, Seward placed in the 

 Cycadofilices, divided into the following sub-classes: 



1. Megaloxyleae 4. Cycadoxyleae 



2. Rhetinangieae 5. Calamopityeae 



3. Stenomyeleae 6. Cladoxyleae 



7. Protopityeae 



The above treatment of Pteridospermae leaves, however, a miscellanea 

 of fronds and seeds which are unclassifiable. In the third edition of his 

 " Studies of Fossil Botany", published six years later than Seward's 

 classification, D. H. Scott employs a different grouping. He does not 

 distinguish between Pteridospermae and Cycadofilices and he distributes 

 the known genera among a series of coequal groups, referred to as " fami- 

 lies " although their name endings are those of tribes. 



