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NOTES ON YORKSHIRE BRYOPHYTES. 



III. REBOULIA HEMISPHERICA (L.) RADDI. 



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



Municipal Technical School, Plymouth. 



The species here dealt with, althoug-h differing- in many respects 

 from the other thalloid or ribbon-Hke liverworts found in 

 Britain, and presenting some peculiar and interesting- features 

 in its structure and biology, has not up to the present time been 

 adequately worked out and described. It is hoped that in this 

 paper botanists may find a fairly complete and straightforward 

 account of this liverwort, based on the writer's own observations 

 of abundant living material. B}^ omitting minute details of 

 development in which this plant does not differ materially from 

 its allies, and by avoiding as far as possible the technicalities 

 which might repel readers who had not given special attention 

 to the liverworts, or hepatica?, as well as by adding a fairly 

 liberal amount of illustrative matter, the writer also hopes that 

 botanical readers in general may find recorded here some 

 interesting points in the biology of this comparatively little- 

 studied group of plants. 



Reboiilia is distributed pretty widely in Britain, but its 

 occurrence in any locality is usually confined to small patches, 

 gTowing on damp soil or rocks. The writer has collected it in 

 considerable quantity on limestone rocks in the Gordale and 

 Malham district, and in Yorkshire, as in other parts of the 

 country, it appears to be practically confined to limestone. 



The flat, ribbon-like thallus (Plate VIII., Fig. i) seldom ex- 

 ceeds 5 cm. (2 inches) in length and i cm. in breadth, and is 

 usually forked repeatedly at the front. The margins are wavy and 

 wrinkled and usually tinged with purple. The upper surface is pale 

 green In colour, and is dotted with numerous small pores, so as to 

 present a granular and finely-netted appearance, very unlike the 

 definite aerolation found in forms like Fegiitella, which grows so 

 commonly besides streams. The growing-point lies in a notch 

 at the front of each branch of the thallus. Besides the ordinary 

 apical branching, the thallus often shows branches arising from 

 the lower surface, usually just below the apex. These ventral 

 branches grow forwards and spread out, and ultimately branch 

 by forking, thus giving the whole plant a jointed appearance 



Naturalist, 



