CONCLUSION 41 



CONCLUSION 



To judge from the foregoing study of Pallavicinia, P. Zollingeri is in 

 some respects more like Morkia than it is like the other species of Palla- 

 vicinia that were examined. This is true of the thallus, which has a broad, 

 indefinite midrib, merging gradually into the wings, instead of the sharply 

 defined midrib, and thin wings of Eupallavicinia. The conducting tissue, 

 however, is well developed. The sporophyte, also, approaches in form 

 that of Morkia. Whether these differences, combined with the very dif- 

 ferent habit, are sufficient to warrant the retention of the generic name 

 Mittenia for the dendroid species of Pallavicinia, may be questioned ; but 

 on the whole we are inclined to think this is justified and the members of 

 the section Eupallavicinia might properly be transferred to Blyttia. 



The inter-relationships of the Jungermanniales are very perplexing. 

 Cavers [2] in his recent excellent summary of the subject points out that 

 there is practically no constant point of difference between the two families 

 Blyttiaceae and Aneuraceae (Schiffner's families Metzgerioideae and 

 Leptotheceae). Cavers places in the first family the genera Blyttia (Pal- 

 lavicinia), Morkia, Symphyogyna and Makinoa. In the latter are also 

 included four genera, Aneura, Metzgeria, Umbraculum and Podomitrium. 

 The two latter are often united into a single genus, Hymenophyton, but 

 they are abundantly distinct and probably not closely related. tUmbracu- 

 lum is undoubtedly related to Metzgeria, but Podomitrium, except for 

 the position of the reproductive organs, is hardly distinguishable from 

 Blyttia, either in the structure of the thallus or that of the sporophyte. 

 P. malaccense, for example, a species common in Western Borneo, is 

 absolutely indistinguishable from a typical Blyttia, except for the position 

 of the reproductive organs upon short ventral branches, instead of upon 

 the ordinary shoots. We believe that Podomitrium should be placed in 

 the Blyttiaceae, rather than in the Aneuraceae, supposing it seems best 

 to retain these two families, and not unite them into a single one as Cavers 

 suggests. 



The production of the reproductive organs upon special branches, 

 which appears to be the only constant difference between the Aneuraceae 

 and Blyttiaceae, seems hardly of sufficient importance to warrant the 

 establishment of two families, especially as, except for the small size of 

 the fertile branches, they do not differ essentially from the ordinary shoots 

 upon which the reproductive organs occur in the Blyttiaceae. 



