MOSSES AND FERNS 



THAP. 



A. 



but there is a rapid lateral growth with results in the formation 

 of two valves, which meet in front much like the two parts of 

 a bivalve shall, and this involucre completely encloses the devel- 

 oping sporogonium. 



In the simplest cases, where the archegonia are borne upon 

 a receptacle 1 which is raised upon a stalk, e.g., Plagiochasma, 

 Clevea (Fig. 20, A), the receptacle does not represent, accord- 

 ing to Leitgeb ( (7) , vi., p. 29), a complete branch, but is only a 

 dorsal outgrowth of the latter, which may grow out beyond it, 

 or even form several receptacles in succession. The first indi- 

 cation of the recep- 

 tacle is a dorsal prom- 

 inence which soon be- 

 comes almost hemi- 

 spherical, and near the 

 hinder margin the first 

 archegonium arises, 

 without, apparently, 

 any special relation to 

 the growing point. 

 On the lateral margins 

 are then formed two 

 other archegonia, not, 

 however, simultane- 

 ously; and finally a 

 fourth may be formed 

 in front : three or four 

 archegonia in all seem 

 to be the ordinary 

 , number. The stalk of 



FIG. 20. A. Clevea sp. A, longitudinal section of 



the thallus showing the dorsal origin of the fe- the receptacle IS 



male receptacle () ; v, the growing point (dia- ^Q. 



gram after Leitgeb) ; B, Reboulia hemispharica 



(Radd.), longitudinal section of very young re- the thallllS, and HOt 3 



ceptacle with the first archegonium () ; x, the J j j- e C t Continuation 



apical cell, X3oo (after Leitgeb). 



of it. 



The next type is that which Leitgeb attributes to Grinialdia, 

 Reboulia, Fimbriaria, and some others, but it is not the type 

 found in Fimbriaria California. In this type the structure of 



appen dage O f 



c 



- The sporongonial receptacle of the Marchantiese is sometimes known as 

 the Carpocephalum. 



