IN PTERIDOPHYTES 



213 



Ophioglossaceae, as in the Marattiaceae, the upright radial shoot is 

 primitive, and the dorsiventral character of the shoot derivative : that in 

 Helminthostachys, as in Danaea and Kaulfussia, all of them heavily-leaved 

 forms in proportion to their relatively elongated stem, the axis has become 

 horizontal. 



The Leptosporangiate Ferns present a more varied and difficult problem as 

 regards the symmetry of the shoot. They include many upright radial forms, 

 such as Cyathea, Alsophila, or Osmunda as well as many which show various 

 degrees of obliquity of the axis, accompanied by corresponding degrees 

 of dorsiventrality. It is not an uncommon thing to find upright radial 



FIG. 109. 



Naked-eye drawing of rhizome of Helminthostachys zeylanica. / r =stipular flap ; R =root ; 

 L leaf; /> = petiole; L S leaf-scar. (After Farmer and Freeman.) 



species, and straggling, dorsiventral species in the same genus : for instance, 

 Onoclea germanica is radial and upright, Onodea sensibilis is creeping ; 

 Pteris aqiiilina is creeping, while many other species are tufted and radial. 

 The same question will arise here as elsewhere, which of the two was 

 the primary condition. From analogy with other cases as well as from 

 internal evidence, the upright, tufted forms with radial symmetry would 

 be held to be the prior type ; but the question is complicated by the fact 

 that the embryo itself is not upright in the Leptosporangiate Ferns, and 

 it may be thought that its recumbent position defines ab initio the dorsi- 

 ventrality of the shoot. 



It is true that the first leaf of the young sporophyte is uniformly on 

 the side away from the prothallus: but the position of the second and 



