70 MOSSES AND FERNS CHAP. 



sorts of rhizoids are present, those that represent the papillate 

 type of the other Marchantiacese, while thicker walled than 

 the others, do not develop the projecting- prominences. Indeed 

 the whole structure of the plant is curiously reduced, and 

 Leitgeb describes it as resembling the young plants of Mar- 

 chantia or Preissia. The development of the sexual organs is 

 but imperfectly known, and the suggestion of Leitgeb' s that 

 possibly the antheridium is reduced to a single cell, seems hardly 

 probable in view of the structure of the rest of the plant. The 

 sporogonium has the stalk and foot exceedingly rudimentary, 

 but the upper part of the capsule shows a zone of cells whose 

 walls are marked by peculiar ring-shaped thickenings, and opens 

 regularly by a number of teeth, which on account of the thick- 

 ened bars upon the cell wall offer a superficial resemblance to 

 the peristome of the Bryales. As in Targionia the archegonia 

 arise near the apex of the ordinary shoots, and no proper 

 receptacle is formed. 



All of the other forms have the archegonia borne upon a 

 special receptacle, which, as the sporogonia develop, is raised 

 upon a stalk. Here belong, according to Schiffner ( i ) sixteen 

 genera with about 150 species. The receptacle may be, as we 

 have seen, strictly dorsal in origin, or it may include the grow- 

 ing point of the archegonial branch, or finally it may be a 

 branch system arising from the repeated dichotomy of the 

 original growing point. 



MONOCLEA 



The genus Monoclea includes two known species, M. 

 Forsteri, found in New Zealand and Patagonia, and M. 

 Gottschci, of Tropical America, said also to occur in Japan. 

 This genus has been usually associated with Jungermanniales 

 (Leitgeb (7), vol. iii., Schiffner (i)), but a more complete 

 study of the plant has shown that its affinities are undoubtedly 

 more with the simpler Marchantiaceae. The structure and posi- 

 tion of the sexual organs, especially the antheridia, and the 

 development of the sporophyte, so far as it has been made out 

 (Cavers (7), Johnson (3)), all point unmistakably to a rela- 

 tionship with the Marchantiacese. 



Two kinds of rhizoids are present, although not so marked 

 as in the typical Marchantiaceae, but the thallus lacks the char- 



