74 REVUE BKYOLOGIOl'E 



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Monoclea is dioecious, and the antheridia and archegonia are 

 developed in sharply defined groups or receptacles. In both cases 

 the sexual organs arc borne on the dorsal surface of the thalhis, 

 and the growing-point, which occupies the front of the receptacle, 

 shows the same large club-shaped mucilage-hairs that are obse^*- 

 vcd at the growing-point of a sterile branch. In bolh cases, too, the 

 first sign of the developing receptacle is a slight swelling on the 

 lower surface of the thallus immediately behind the growing-point 

 and a corresponding depression on the dorsal surface, and it is 

 hardly possible at first to distinguish the two kinds of receptacle, 

 except in sections. 



The fully developed male receptacle strongly resembles that of 

 Fegalella in general appearence (Fig. 1, A.). It is oval in outline, 

 about 8 mm. long and 3 mm. broad, and is sessile, its upper sur- 

 face projecting slightly above the thallus and'bcaring numerous 

 slight prominences. In some cases the receptacle occupies the end 



of a branch, as in Fegalella or Jleboulia^ but more frequently it 

 stands on the middle of the thallus at a considerable distance from 



the growing-point of the branch. Evidently, therefore the gro- 

 wing-point is n,ot used up in the development of the receptacle, 

 but resumes its ordinary vegetative growth after the receptacle 

 has been formed and mny give rise to several receptacles in suc- 

 cession. 



The early stages in the development of the receptale closely 

 resemble those observed in Fegalella and RebouUa, Tlie anther- 

 idia are developed in acropetal succession and at first occupy 

 a depression in the upper surface of the thallus, immediately 

 behind the growing-point. Each antheridimii becomes sunk in 

 a deep cavity, formed by the active growth of the surrounding 

 tissue. This cavity is continued above into a canal, which opens 

 by a pore occupying one of the conical prominences on the 

 upper surface of the receptacle (Fig. 3, A.). In a vertical section 

 through a fully developed receptacle three w^ell-marked zones 

 may be distinguished: (1) an upper narrow zone of green tissue, 

 consisting of small polygonal cells with abundant chloroplasts ; 

 (2) a broad middle zone of colourless tissue, in which tjie anther- 

 idia are embedded and which consists of very large, loosely 

 arranged cells ; (3) a lower zone which lies below the antheridia 

 and consists of the ordinary tissue of the thallus, containing oil- 

 bodies and bearing on its lower surface numerous wide, thin- 

 w^alled rhizoids. The cells of the colourless tissue, forziiing the 

 greater part of the thickness of the receptacle, at first contain 

 abundant starch-grains, but later become highly mucilaginous 



