98 DIFFICU1.TIES AND SOURCES OF ERROR. [CH. 



Endless examples might be quoted illustrating the absolute 

 futility, in many cases, of relying on external features even for 

 the purpose of class distinction. An acquaintance with the 

 general habit and appearance of only the better known members 

 of a family, frequently leads to serious mistakes. The specimen ' 

 shown in fig". 22 is a leaf of a tropical fern Kaulfussia, a genus 

 now living in South-eastern Asia, and a member of one of the 

 most important and interesting families of the Filicinse, the 

 Marrattiacese ; its form is widely different from that which one 

 is accustomed to associate with fern fronds. It is unlikely that 

 the impression of a sterile leaf of Kaulfussia would be recognised 

 as a portion of a fern plant. 



Similarly in another exceedingly important group of plants, 

 the Cycadaceae', the examples usually met with in botanical 

 gardens are quite insufficient as standards of comparison when 

 we are dealing with fossil forms. Familiarity with a few 

 commoner types leads us to regard them as typical for the whole 

 family. In Mesozoic times cycadean plants were far more 

 numerous and widely distributed than at the present time, and 

 to adequately study the numerous fossil examples we need as 

 thorough an acquaintance as possible with the comparatively 

 small number of surviving genera and species. The less common 

 and more isolated species of an existing family may often be of 

 far greater importance to the palseobotanist than the common and 

 more typical forms. This importance of rare and little known 

 types will be more fully illustrated in the chapters dealing with 

 the Cycadacese and other plant groups. Among Dicotyledons, 

 the Natural Order Proteacese, at present characteristic of 

 South Africa and Australia, and also represented in South 

 America and the Pacific Islands, is of considerable interest to 

 the student of fossil Angiosperms. In a valuable address 

 delivered before the Linnean Society^ in 1870 Bentham drew 

 attention to the marked ' protean ' character of the members 

 of this family. He laid special stress on this particular division 

 of the Dicotyledons in view of certain far-reaching conclusions, 

 which had been based oh the occurrence in different parts of 

 Europe of fossil leaves supposed to be those of Proteaceous 

 ' Dealt with more fully in vol. ii. 2 Bentham (70). 



