202 Alc.vaiidcr IV. Evans, 



their walls. In HymenopJiytum, according to the published 

 accounts, the elaterophore is even less developed and the irregular 

 thickenings of the capsule-wall are restricted to the layer on the 

 outside. 



The genus Podoinifriitin contains only two species, P. pliyl- 

 lanthus (Hook.) Alitt. of New Zealand and P. molaccense (Steph.) 

 Campbell (3) of the Malayan region. It is placed by Cavers in the 

 Aneuraceae and agrees with Hymcnophytum in having the sexual 

 organs borne on specialized ventral branches and in developing a 

 pseudoperianth. The sexual branches, however, are much better 

 developed. The male branch shows a double row of antheridia, 

 each protected by a scale, and the female branch develops a laciniate 

 involucre around the archegonia. The thallus, moreover, is not 

 highly differentiated like that of Hymcnophytum, but is prostrate 

 and consists (except for the short stalk-like base) of a flat strap- 

 shaped expansion, in which the thickened median portion thins out 

 gradually into unistratose wings. In the thickened portion a 

 strand of narrow thin-walled cells is present, and even the vege- 

 tative branches are mostly ventral in origin. The most important 

 differences, however, are found in the capsule, which lacks an 

 elaterophore completely and shows a wall two or more cells thick 

 without local wall-thickenings, the radial walls of the outer layer 

 being uniformly thickened. In Campbell's opinion these diff'erences 

 are not only sufffcient to separate Podomitrium generically from 

 Hymcnophytum but to show that its true affinities are with Pal- 

 lavicinia, the largest genus of Cavers's family Blyttiaceae. 



In the genus Pallavicinia, as typified by the widely distributed 

 P. Lycllii (Hook.) S. F. Gray, the thallus is essentially like that 

 of Podomitrium and the same thing is true of the capsule. The 

 two genera agree further in the protective scales covering the 

 antheridia, in the laciniate involucres around the archegonial 

 clusters, and in the pseudoperianths around the young sporophytes. 

 The sexual organs of Pallavicinia, however, instead of being 

 borne on specialized ventral branches, arise in median groups on the 

 dorsal surface of ordinary branches. Although such species 

 as P. Lycllii agree with Podomitrium in the features of the 

 thallus, the genus contains other species which agree better 

 in these respects with Hymcnophytum. These are the so-called 

 dendroid species and are known only from tropical, south temperate 



