70 



ANALYSIS OF THE SHOOT-SYSTEM OF FERNS [CH. 



and Davallia, and they have long been known in Dryopteris, Polypodiiun, 

 Pteridium, and many others. Dichotomy has also been recorded among 

 early fossils, such as Botrychioxylon and the Botryopterideae. These examples 

 serve to show that distal dichotomy of the axis is widespread among Ferns. 

 Moreover, while it appears in some advanced types, it is frequent among 

 primitive types now living, and has been recorded among early fossils. 



(H) Other Ferns show buds in a position seemingly very different from 

 those produced by dichotomy. The axillary position is not uncommon, and 

 it is found in some of the most archaic types. Among living Ferns it is best 

 seen in the Hymenophyllaceae (Fig. 63). It has been shown to occur in the 

 Ophioglossaceae, being first demonstrated in them by Gwynne-Vaughan(48) 

 for Helminthostachys (Fig. 64), and later by Lang(47) for Botiychiuni. In them 



Caned. 



Fig. 63. Trichoniaiies radicans, longitudinal 

 section of the apex {ap), with axillary bud 

 {ax), and subtending leaf (/). ( x 20.) 



Fig. 64. Longitudinal section through 

 a leaf-insertion of Helminthostachys, 

 showing the petiole {pet) and stipule 

 (st), in the axil of which a canal arises 

 leading obliquely down to a dormant 

 bud. (After Gwynne-Vaughan.) 



the position of the bud is comparable to that which is prevalent in Flower- 

 ing Plants. It has also been shown to exist in such early fossils as the 

 Zygopterideae, and in the Pteridosperm, Lyginopteris (Brenchley (57)). The 

 physiological advantage in respect of nutrition and protection which the 

 axillary relation with the leaf affords may probably account for that position 

 of the bud being adopted, and persistently maintained in certain groups, as 

 it is regularly in Flowering Plants. 



(Ill) Buds may also be formed in extra-axillary positions related to the 

 leaf-base, particularly on the abaxial side of it. This position is often a 

 definite one, and is well seen in Lophosoria, Metaxya, CheiropleiiriaiY'ig.S^), 

 E lap hoglos Slim, and in Cibotiuin Barometz. The vascular connection appears 

 in these cases to be rather with the leaf-trace than with the supply of 

 the main axis, though it is difficult to draw any clear line between these. 

 The physiological convenience of a bud which can thus tap the stream of 



