56 



MOSSES AND FERNS 



EHAP. 



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^ 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- 



A. 



WpJWWWW 



B. 



tacle is a dorsal prom- 

 inence which soon be- 

 comes almost hemi- 

 spherical, and near the 

 ^ V. hinder marein 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 

 . ^, . A , .. J. 1 .. t number. The stalk of 



Fig. 20. — A. Clevea sp. A, longitudinal section of 



the thallus showing the dorsal origin of the fe- thc rCCCptacle is alsO 



male receptacle ($) ; v the growing point (dia- ^ ^^^.g^j appCudagC of 

 gram after Leitgeb) ; B, Rebouba hemtsphcenca ^ ^ "^ 



(Radd.), longitudinal section of very young re- thc thalluS, and UOt 3, 



ceptacle with the first archegonium C^) ; x, the r\ { r q n f COntiuUation 

 apical cell, X300 (after Leitgeb). 



of it. 

 The next type is that which Leitgeb attributes to Grimaldia, 

 RebouUa, Fimhriaria, and some others, but it is not the type 

 found in Fimhriaria Calif ornica. In this type the structure of 



 The sporongonial receptacle of the Alarchantiese is sometimes known as 

 the Carpocephalum. 



