436 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



stem. It has a sessile proper involucre. The spores, according 

 to Montagne, are solitary, and strongly echinulate. They are 

 not mature in my specimens, and in this condition are per- 

 fectly smooth. In Sphcerocarpus, Riccia, and many other 

 Acrogens, on the contrary, four spores are formed from the 

 contents of one mother cell. They present, therefore, as 

 the division is not equatorial, three plane and one convex 

 surface. One species occurs in Algiers, the other in Sar- 

 dinia. Riella, like Subularia, bears fruit under water ; 

 but in the aquatic Riccice fruit is rare, except where the 

 fronds are stranded on the bank. I am not aware that 

 any of the species can rank as more than mere botanical 

 curiosities. 



479. These plants are subject to considerable variation both 

 in the breadth and division of the fronds, and the degree of 

 projection of the sporangia. The scales also, with which many 

 are clothed, are by no means constant in size and form, or even 

 in number; though, perhaps, in species of which they are cha- 

 racteristic, they never fail entirely, except from accident, as 

 I have seen to be the case in Riccia natans. 



11. Marchantiace^, Cord. 



Marchantie^e, Wees ab. Esenh. CEPHALOTHECiE, Cephalothecia, 

 Dumort. 



Sporangia valvate or bursting irregularly, for the most part 

 disposed symmetrically on the under side of pedunculate rotate 

 receptacles, mostly arising from the transformed margin of the 

 frond ; rarely solitary and sessUe : peduncle often sheathed or 

 involucrate. Spores mixed with elaters. Antheridia contained 

 in proper sessile or pedunculate, peltate or discoid receptacles. 

 Cuticle areolate, porous. 



480. The distinctive character by which these Hepaticce are 

 known from Ricciacece, consists in the elaters with which the 

 spores are mixed. These are no less conspicuous in Junger- 

 mannice, but the sporangia are always sohtary in that order, 

 though they are evidently connected with Marchantiacece, by 

 means of Lunularia (Fig. 93, d). Mr. Henfrey has very care- 



