242 



NOTES ON YORKSHIRE BRYOPHYTES. 



III. REBOULIA HEMISPHERICA (L.) RADDI. 



F. CAVERS, D.Sc.(LoND.), F.L.S., 



Municipal Technical School, Plymouth. 



(Continued from p. 214.) 



Reboidia may be said as a general rule to prefer moist and 

 shaded situations, though occasionally patches of this plant 

 occur in somewhat dry and exposed places. The thallus is, in 

 the latter case, capable of resisting a fairly long period of 

 drought, during which the margins become rolled inwards, and 

 growth may be resumed after the plant has been kept dry for 

 several weeks. 



Colonies of the blue-green alga Nostoc are frequently found 

 between the ventral scales and the lower surface of the thallus, 

 and occasionally also in the cells of the compact tissue of the 

 midrib. Nostoc and other endophytic (perhaps symbiotic) algse 

 have long been known to inhabit specialised organs in certain 

 liverworts {Blasia, Anthoceros), and the writer has observed the 

 occurrence of the coiled chains of Nostoc in the tissues of 

 Fegatella, Preissia, and Targionia, in addition to Rehoulia. 



The two kinds of sexual organs (antheridia and archegonia) 

 are sometimes developed on the same plant, but more commonly 

 on distinct plants. Both are formed in groups on specialised 

 branches (receptacles), and both kinds of receptacle arise 

 immediately behind the apex of a branch, on the upper surface 

 of the thallus. In monoecious plants, one of the branches 

 arising from a dichotomy gives rise to a male and the other to 

 a female receptacle (Fig. i, B.). 



The MALE RECEPTACLE is scssile and forms a green cushion, 

 oval, circular, or semilunar in outline (Fig. i, h.. B.). The 

 receptacle is slightly raised above the general surface of the 

 thallus, and is marked off by a deep groove, from which arise 

 numerous narrow scales, usually reddish in colour. The upper 

 surface of the receptacle is marked by blunt conical prominences, 

 each showing a very small pore surrounded by numerous con- 

 centric rings of cells (Fig. 4, E.). Each pore leads into a 

 canal which widens out below to a cavity containing a single 

 antheridium (Fig. 4, A., B.). In the upper part of the recep- 

 tacle the cells contain chloroplasts, and there are numerous 



Naturalist, 



