66 



a regular rhomboidal dodecahedron have never occurred to 

 me : I do not even think that there is any actual similarity. 



The Riccice, like all plants having a tissue consisting of se- 

 veral layers, possess a cuticle, i.e. an upper cellular layer, and 

 M. Lindenberg observes very justly that it is merely a dis- 

 pute about words, whether the epidermis ought to be consi- 

 dered as a distinct organ or merely as the upper cellular layer 

 of the parenchyma. The form of the cells of the epidermis 

 of the RiccicB is more or less regular dodecahedral, of which, 

 however, I could not convince myself. The cells of the epi- 

 dermis are filled with green sap globules when the frond is 

 quite thin, but uncoloured when the frond is more consider- 

 able, and the green cells then gleam through the interior of 

 the frond, and in this way originates the greyish green colour, 

 when dried silvery grey, which for instance is peculiar to R. 

 glauca. At times the marginal cells are provided with cellu- 

 lar sap and even amylum granules occur in them. The rough 

 surface of the Riccice is caused by small verrucous swellings 

 of the upper sides of the cells. " Frequently," observes M. 

 Lindenberg, " these vesicular prominences are and remain 

 closed ; not unfrequently however they open on the further 

 development of the plant ; either quite irregularly, as in R. 

 hortorum, crystattina, the upper cellular sides disappearing al- 

 most entirely, and thus irregular cavities of various size and 

 open above originate ; or by the disintegration of some cells 

 round or oval fissures are formed, as in Corsinia marchan- 

 tioides ; or lastly by some cells raising themselves higher and 

 in the shape of warts, and these apparent papillae open above as 

 in Ricciafimbriata." In Oxymitra the apertures are surround- 

 ed regularly by smaller round cells. All these observations are 

 exceedingly interesting, especially on account of the similar 

 appearances which have here and there already been noticed 

 in plants. I compare the apertures, with and without pa- 

 pillae-like prominences of the adjacent cells of the epidermis, 

 which M. Lindenberg has observed, to the so-called stomata 

 of the Marchantice ; the papillae of Riccia fimbriata especially 

 bear the greatest resemblance to the open prominences on the 

 fronds of the Marchantia, in which the true cuticular glands 

 which present the stoma in the centre of their two semicir- 



