CH. XXl] 



HABIT 



127 



stock. This may sometimes extend to a height of several feet in Todea 

 Barbara: the habit is then that of a stunted tree-fern. Compton states 

 {Linn. Joiirn. xlv, p. 456) that Leptopteris Wilkesiana Christ may reach a 

 height of 10 feet in New Caledonia. The leaves expanded in the current 

 form together a basket-shaped group, the outermost of which are often 

 sterile and the inner fertile. Some of the leaves at the outside of the winter 

 bud have an abortive lamina, while their broad persistent basal region acts 

 as a protection. The leaves have the usual circinate vernation, and are 

 covered while }^oung with a dense mat of hairs, which fall off at maturit}'. 



The leaves are pinnate with varying degrees of branching: but the 

 juvenile leaves show clearly how that state is referable to sympodial 

 development of dichotomy (Fig. 416), This same method continued in 



Fig. 416. Successive juvenile leaves of Ostmaida regalis, showing steps {a — g) 

 of progression from equal dichotomous venation to sympodial branching, and the 

 establishment of a terminal lobe. ( x 2^. ) 



successive branchings will explain the structure of the most complicated 

 leaves. The broad protective leaf-base is a feature of importance for com- 

 parison. The wings of the petiole are traceable downwards into broad flaps, 

 or "stipular leaf-bases," forming together with the mucilaginous hairs a very 

 perfect protection to the young parts. In Todca their development extends 

 also to a transverse commissure across the face of the leaf-stalk. Commissures 

 are unknown in Leptosporangiate Ferns: but they occur in the Ophio- 

 glossaceae and Marattiaceae, while like structures appear also among the 

 Cycads. Such stipular leaf-bases are archaic features. Kidston and Gwynne- 

 Vaughan have shown how similar leaf-bases are characteristic also of the 

 fossils referred by them to an Osmundaceous affinity {Fossil Osninndaceae, 

 Part I, Plate VI). The texture of the leaf-blade may be leathery or filmy. 



