246 



Cavers : Notes on Yorkshire Bryophytes. 



arise numerous long narrow scales, each ending- in a club-shaped 

 mucilage-hair. These scales are arranged in three or four con- 

 centric rows, and each appears to arise from a single superficial 

 cell. The archegonia at first stand at the sides of the receptacle, 

 but they soon become displaced owing to the active growth of 

 the dorsal tissue, and are carried down to the lower surface. 

 The growing-point is seen in the earlier stages occupying the 

 front of the receptacle, but when the latter is fully formed the 

 growing-point becomes used up in the formation of the stalk, 

 which shows a single ventral furrow. During the development 

 of the archegonia the tissue of the receptacle becomes differen- 

 tiated into an inner region of compact colourless tissue and an 

 outer region of green tissue with large air-chambers. The 

 pores by which the latter communicate with the exterior are 

 very conspicuous in the fully-developed receptacle, each pore 

 being surrounded by eight or nine tiers of cells, the uppermost 

 cells being very small and the lowest very large (Fig. 6, A.). 

 The large cells of the lowest ring are capable of changing in 

 form so as to partially close the pore. On treating fresh pre- 

 parations with salt solution these cells become plasmolysed and 

 the lower opening of the pore is greatly diminished in size. 

 The cells of the epidermis have thick outer walls and contain 

 little or no chlorophyll. 



As the archegonia are carried on to the lower side of the 

 receptacle, the surrounding tissue grows actively so as to form 

 a sheath (involucre) around each of them. The margin of each 

 sheath continues to grow downwards, becoming thinner and 

 more membranous towards the margins. When the archegonium 

 is ripe its neck projects beyond the opening of the involucre, 

 curving upwards, and is surrounded by the numerous scale-like 

 hairs, which serve to retain the moisture necessary to the open- 

 ing of the archegonium neck. 



The margin of the mature receptacle shows from five to 

 eight (generally six) lobes, each lobe corresponding to an arche- 

 gonium (Fig. I, B., C). Between the lobes there grow out, on 

 the lower surface of the receptacle, bundles of tuberculate 

 rhizoids, most of which pass into the furrow on the anterior 

 (ventral) surface of the receptacle-stalk (Fig. 5 ; Fig. 6, A.). 

 The lower surface of each lobe shows the two lateral valves of 

 the involucre, which overlap each other, and beyond which the 

 capsule ultimately protrudes. 



Up to the time when the archegonia are ready for fertilisation 

 the growing-point of the shoot is recognisable in front of the 



Naturalist, 



