236 



MOSSES AND FERNS 



CHAP. 



from the upper side of the thallus the reproductive organs are 

 developed. Numerous rhizoids grow from the superficial cells. 

 Mettenius (2) has described the gametophyte in O. pedun- 

 culosum, which agrees in the main with that of O. pendulum. 

 In this species, however, there is first developed a ''primary 

 tubercle" (Fig. 125, B), and the branches were observed in 

 some cases to grow above the ground, where they became flat- 

 tened and developed chlorophyll. 



Fig. 125. — A, B, Prothallia of Ophioglossum pedunculosum, Xi/4; B, shows the 

 young sporophyte, with the cotyledon and first root, r; t, the primary tubercle. 

 C-F, O. pendulum. C, An old prothallium, X6; D, nearly ripe antheridium; E, 

 surface view of antheridium, showing the opercular cell; F, nearly ripe arche- 

 gonium; D-F, X about 275; (A, D, after Mettenius; C-F, after Lang). 



The Sex-Organs 



The antheridium arises from a superficial cell which divides 

 by a periclinal wall into an inner cell, from which by further 

 divisions the mass of sperm-cells is derived, and an outer one, 



