43 



PINNi^, PINNULES, AND PINNULETS. 



It is a curious fact that although the fronds of all Ferns, 

 like the leaves of all flowering plants, perform the same 

 function, namely the provision of cellular surfaces adapted 

 to catch the light direct or diffused of the Sun, and by 

 virtue of the energy thence derived to absorb the carbonic 

 acid gas in the air, and in conjunction with the earthy 

 salts obtained through the root system, to build up the 

 plant and its various products, they have assumed an 

 extraordinary diversity of form. Thus in our com- 

 paratively few native species, we have examples of the 

 simplest kind in the Hartstongue, with its simple 

 undivided, smooth-edged, sword-shaped fronds, and at the 

 other end of the scale the much divided ones of the Lady 

 Fern with an almost incalculable number of sub-divisions. 

 For the purpose of indicating the grade of such sub- 

 divisions they have been named : (i) the pinna, or first 

 lateral outgrowth from the midrib ; (2) the pinnule, or 

 secondary division, which springs from the midribs of the 

 pinna; and (3) the pinnulet, which stands in the same 

 relation to the pinnule. In some of the more highly 

 developed abnormal plumose forms we arrive at even a 

 fourth stage, viz. divisions of the pinnulets, which may be 

 termed pinnuletines, farther than which it is needless to 

 go by way of diminutives. 



On close examination it is seen that as a rule these 

 various grades of sub-division are really reductions of the 

 plan of the frond itself, each grade doing its best to assume 

 frond form on a smaller scale, the vein system always 

 pursuing the same plan and angles of growth. Hence 

 when, as has frequently occurred, a normally once- 

 divided species sports into more divided forms, the pinnae 

 tend more and more to assume the form of smaller fronds. 

 Our common Polypody P. vidgave, lor instance, has produced 

 several grades, viz. P. v. semilaceYiiui, which as a section 

 varies from merely saw-toothed pinnae to bipinnate ones, 



