434 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



Oxymitra 'pyramidata and Corsinia Marcfmntioides. In 

 some species of Riccia* there are many air passages between 

 the cells, besides the .large cavities in which the archegonia are 

 produced. The species are either terrestrial, epiphytous, or 

 aquatic ; and the same species may assume each of these 

 habitats, with slight alterations in consequence of the change. 

 The under surface is often beset to a greater or less extent with 

 thin scales, which are especially remarkable in Riccia natans 

 (Fig. 89, h).-f In some species the margin is ciliated. The 

 species have a wide extent, but are more numerous in Europe 

 than elsewhere, especially towards the south. Riccia coch- 

 leata of the Antarctic Flora is a doubtful species. Unfor- 

 tunately it was not found with fruit, and therefore its true 

 affinities are obscure. It approaches by its lobed margin to 

 Jungermannice. Three species occur in New Zealand, and 

 several at the Swan River. Oxymitra differs from Riccia, 

 in the more prominent fruit, and in having a proper invo- 

 lucre, though it has no common involucre, while Corsinia has 

 the habit of Marchantia and superficial fruit, with a common 

 paleaceous di- or pluri-phyllous envelope. Both these genera 

 belong eminently to the south of Europe, extending in the 

 second instance as far as the Canaries. There is, however, in 

 Sir W. J. Hooker's Herbarium, a species marked Riccia para- 

 doxa (Fig. 91, a), gathered in Brazil by Gardner.^ Each 

 sessile globose sporangium has a di-triphyllous involucre, con- 

 sisting of broadly ovate leaflets clasping the fruit, without any 

 foliaceous scales or divisions. This should certainly form a 

 distinct genus ; for it is not, as was supposed, concocted from a 

 Riccia and a Corsinia. The involucre is not general, but 

 partial and of a different order, therefore, from that of Corsinia. 



* See Unger in Linn., vol. 13, tab. 1 . These air passages do not, how- 

 ever, exist in every species. 



t The scales in Riccia natans are a most beautiful microscopical 

 object when treated with different chemical tests, from their transpa- 

 rency and variety of colouring. 



I See Hook. Lond. Journ., vol. 3, p. 166. As it is quite clear that it 

 is no Riccia or Corsinia, and is more nearly allied to Sphcerocarpus than 

 to either, I beg leave to propose for it, as a generic name, Cronisia. 



