20 ON GENERA AND SPECIES. 



sporangia, to which the term paraphysis is given. In 

 Ampliidesmium, Lophosoria., Trichopteris^ and several species 

 of Alsophila, numerous simple or articulate hairs are mixed 

 with the sporangia, which impart to the sori a woolly or 

 hirsute appearance. 



The above is a general view of the form and position of 

 the different organisation of Ferns, and furnishes data for 

 the definition of genera and their arrangement ; but as in 

 many instances of botanical definitions, there are always 

 exceptions to normal forms and position of parts, even to 

 the sori being produced on the under side of the frond, as 

 in Polysticlium anomalum, a native of Ceylon ; in some of 

 its fronds the sori are as abundantly produced on the upper 

 side as on the under, and bear the characteristic peltate 

 indusium. The same also occurs in TricJiiocarpe Moorei, a 

 native of New Caledonia. Such seems to be the normal 

 state of these two species even in native specimens, as 

 also in plants cultivated in Kew. 



3. ON THE GENERA OF EARLY AUTHORS AND THEIR SYSTEMS 

 OF CLASSIFICATION. 



HAVING described the principal organs of Ferns, by means 

 of which genera are defined and classified, I now proceed 

 to give a brief review of the progress of Pteridology from 

 the time of Linnaeus to the present, noting' the works of 

 the principal systematic authors who have from time to 

 time collated and characterised the genera and species of 

 Ferns at their respective periods. 



It appears that only about one hundred and ninety 

 species were known to Linnaeus. These he classified 

 under eleven genera viz. : Osmunda, Onoclea, Acrostichum, 



