GENERAL RESULTS— PTEROPSIDA 639 



vegetative and reproductive, point in this direction, and 

 the evidence has been materially strengthened by the 

 observation of spores in process of germination, agree- 

 ing closely with corresponding early stages in the 

 development of recent Fern prothalli (p. 339). 



Anatomically, the Botryopterideae show two types 

 of structure, the one {Botryopteris and its allies, p. 325) 

 exceedingly simple as regards the stem-structure, while 

 the other {Zygopteris and its allies, p. 306) shows a con- 

 siderable degree of differentiation. The solid strand of 

 tracheides, surrounded by phloem, which constitutes 

 the central cylinder in the Botryopteris group, is perhaps 

 the simplest form of stele known in any Fern, but it 

 would be rash to infer from this fact that these plants 

 were necessarily of a specially primitive nature. Their 

 roots are diarch, like those of most recent Ferns, their 

 petioles attain some degree of complexity in vascular 

 structure, while the differentiation of special fertile 

 fronds indicates a rather high grade of organisation. 



The affinities of the Botryopterideae with other Ferns 

 have been fully discussed in Chapter IX., "and the conclu- 

 sion arrived at, that while they show some affinity with 

 various Filicinean families of later origin, they cannot 

 be considered as on the direct line of their descent. 

 This line will have to be sought among other Primo- 

 filices, of which, as yet, we have only a scanty know- 

 ledge, though the occurrence of annulate sporangia on 

 ordinary Fern pinnules, as in Pteridotheca Wittiamsonii, 

 is a promising indication (p. 293). 



Some relation between the Botryopterideae and the 

 Ophioglossaceae was recognised by Renault when he 

 first discovered the fossil family, the resemblances he 



