192 BLECHNOID FERNS [CH. 



such as the epiphytic Heteropteris and Hy^nenolepis, may now find a definite 

 place elsewhere (see p. 222). The remainder, including Taenitis itself, may be 

 provisionally regarded as ''genera incertae sedis." For the present purpose 

 it is best to confine the discussion to those genera of which the relations to the 

 Blechnoid Ferns are generally accepted: but it seems appropriate to remark 

 that semi-xerophytic types, such as the Blechnoid Ferns are, might be 

 expected to adopt an epiphytic habit, and to undergo such consequent 

 modifications as would make the recognition of their affinity difficult. 



Comparison 



The Blechnoid Ferns, cleared as above suggested of doubtful allies, form 

 a coherent series based upon a relatively xerophytic character of the vegeta- 

 tive system, with dimorphic leaves and open venation. The dermal appendages 

 are broad scales and hairs, with a large distal glandular cell. Two coenosori 

 run one on either side of the mid-rib of the narrow fertile pinna: and they are 

 closely invested by the recurved margins. These broad features of the section 

 Lomaria, including those also of the vascular system, are all in accord with 

 what is seen in Matteiiccia, excepting that Lomaria has coenosori in place of 

 separate sori. But it has been seen that in M. intermedia the indusium is 

 absent, while the separate circular sori are disposed in regular intra-marginal 

 rows, A lateral fusion of such sori, together with the formation of a vascular 

 commissure linking the veins together beneath the receptacle, is all that is 

 wanting to convert the type of M. intermedia into that of a simple Lomaria. 

 In both the sori themselves are basipetal, as they are in Alsopkila, where also 

 they are often disposed in parallel lines, but without the recurving of the 

 pinna-margin. From such facts it is concluded that the simple type of 

 Lomaria originated by soral linkage from a non-indusiate type such as that 

 of M. intermedia. A similar soral linkage has been seen to have occurred 

 repeatedly among the Dicksonioid-Pteroid Ferns, where the sori are marginal : 

 but here they are superficial in origin, as they are in the whole Cyatheoid 

 series and their derivatives. The conclusion seems then clear that the struc- 

 tural advance to soral linkage has been homoplastic in the marginal and the 

 superficial series; resulting in the one case in Pteroid, in the other in 

 Lomarioid t3^pes of Ferns. Both have been successful innovations, as 

 measured by number of species. 



The type oi Lomaria was also successful as shown by the wide geographical 

 spread of the numerous species. But it suffered from the disability that 

 nutritive material elaborated by the trophophylls had to be transferred 

 from the point of production, through the leaf-base and axis, to the sporo- 

 phyll. An obvious amendment would be to secure to the attenuated sporophyll 

 the power of self-nutrition sacrificed to the protection of the naked sori. This 

 relaxation of a xerophytic feature would naturally follow on life under less 



