ON GBNEEA AND SPECIES. 21 



Semionitis, Polypodliim, Asplenium, Pteris, BlecJinum, Lon- 

 chites, and Trichomanes. The data upon which, they were 

 founded were derived, as in flowering plants, from the 

 different modifications and position observed in their so- 

 called organs of fructification. The chief difference con- 

 sisted in the fructification — spore cases or sporangia — being 

 produced either in defined round masses, or in lines, or 

 densely crowded together on the under side of the frond, 

 or in simple spikes or panicles formed by the whole or a 

 portion only of the fertile frond being contracted. Thus, 

 according- to Linnreus' characters, all Ferns having their 

 fructification in simple or racemose spikes belong to 

 Osmunda and Oiioclea ; in crowded masses to Acrostichum ; 

 in round masses or sjjots to Polypodium ; in lines across 

 one another to Hemionitis ; in lines diverging from the 

 mid-rib to Aspleniuin ; in a line on each side of the mid-rib 

 to Bleohnum ; in a Ime or dots on the margin to Pteris and 

 Adiaiitiim ; in a sinus on the margin to Lonchites ; and 

 inserted on the margin to TricJwmaiies. 



These Linnean g-enera are each composed of a greater 

 or lesser number of species, each of which is presumed to 

 agree in the form and position of the fructification with the 

 respective g-eneric characters as above stated. But the 

 more careful examination by later observers of the same 

 generic forms has revealed additional variations, which 

 will come under notice as we proceed. It is worthy of 

 remark, however, that the whole of the species of Ferns 

 now known are capable of being referred to Linnean 

 genera ; but if such were done, species possessing very 

 different appearances as regards habit and mode of growth 

 would be brought together, and the g-onera would be of 

 unwieldly dimensions. 



The first author of importance after Linnasus was Dr. 



