FERN ALLIES OP NEW ZEALAND. 



that of the Polypodiwm, it is yet a similar organ, only very much 

 contracted. The fronds, also, are very different in appearance, and 

 are distinctly of two forms (hence called dimorphic) ; one of these 

 (fig. B 6) being the sterile or barren fronds, and the other (fig. B 6) 

 being the fertile, or spore-bearing. The function of the barren 

 fronds being chiefly to aid in the nutrition of the plant, they are 

 tolerably large and well developed, while the sterile ones are reduced 

 to the smallest size compatible with the production of the numerous 

 spore-capsules developed on them. Instead of having a .single blade, 

 or lamina, on their short stipes, both forms have a number of separate 

 small blades or leaflets (the pinnce) arranged along the midrib of 

 the frond, which is in this case called the raclds. This rachis is 

 not smooth and polished as is the stipes of the Polypodium, but is 

 clothed throughout with slender, pale-brown scales. The pinnae, 

 which are either opposite or alternate with one another, approximate 

 together till at the veiy apex of the frond they are in close contact, 

 and their bases are said to be decivrrent, as they form a wing on the 

 rachis. A frond bearing such pinnae is said to be p)innate, except at 

 the very top, where — the leaflets having become continuous— it is only 

 pinnatifid. The separate pinnse in the right-hand frond are oblong 

 in shape, while the broadest of those on the left are broadly-elliptical ; 

 both have their margins minutely toothed. If we examine the 

 underside of one of these pinnse, we notice a midrib having a few 

 scales on it, and from it a number of fine veins branch, each of which 

 divides almost at once into two equal and nearly parallel arms, like 

 the two branches of a tuning fork. This mode of branching in two's, 

 whether it occurs in veins (PL IV. fig. 2) or in the branches 

 themselves (PI. IV. fig. 1), is termed dichotomous. No traces of 

 sori are to be found on these pinnse, and the frond is therefore 

 termed sterUe. 



The other fronds of this same plant (fig. B 5) are very different 

 in appearance, owing to the pinnse being extremely narrow, and to 

 their standing almost parallel with the rachis. On turning up the 

 underside of one of these pinnse, it will be seen that the margins are 

 turned back very completely, and in the hollow thus formed the 

 capsules are crowded in a dense, continuous line. The recurved 

 edge of the frond thus forming a covering to the confluent sori is 

 termed the involucre or indusium. (An enlarged section of the 



