THE HIGHER CRYPTOGAMIA. 113 



not reach quite to its base ; it projects in the form of a 

 blunt knob into the indentation of the fore edge of the last 

 vegetative shoot (PI. XII, fig. 17). 



The differentiation of the tissue of the leafy, expanded, 

 vegetative shoots is not continued into the stem of the fruc- 

 tifying shoot. At the point where it is attached to the next 

 older shoot the upper side of the stem decreases by a steep 

 inclination to the extent of the height of the layer which 

 bears the air-cavities (PL XV, fig. 12 ; PI. XVI, fig. 17). 



The archegonia spring from the lateral margins of the 

 receptacle in the form of cylinders of cellular tissue directed 

 obliquely upwards (PL XV, fig. C). The essential features of 

 their development and structure correspond with those of 

 the J linger manniee and the mosses. Very soon after the 

 appearance of the archegonia the portion of the receptacle 

 above them begins to grow considerably in breadth, and 

 also downwards. The archegonia, in consequence, appear 

 shortly afterwards to be situated on the under side of the 

 expanded receptacle (PL XV, fig. 11; PL XVI, fig. 7). The 

 receptacle of Rebouilla hemispherica usually produces onlv 

 four archegonia ; sometimes one more, frequently less. The 

 cells of the upper surface of the ventral portion of the 

 archegonium divide at an early period by septa parallel to 

 the axis ; even before the bursting of the apex the central 

 cell is surrounded by a double layer of cells (PL XVI, 

 fig. 17). The neck is considerably bent upwards. The ex- 

 pansion of the receptacle above the archegonia takes place 

 at a late period compared with the other Marchantieae, 

 i. e. not till after the opening of the apices of the arche- 

 gonia. The growth of the margin of the receptacle down- 

 wards is at first more vigorous between the archegonia than 

 above them. 



In the neighbourhood of impregnated archegonia these 

 circumstances are altered. The tissue of the receptacle 

 above them increases in mass not less actively than in their 

 neighbourhood. Afleshysheath is formed, encircling the fore 

 part and sides of the swollen ventral portion of the arche- 

 gonium. Behind the young calyptra also the margins of the 

 sheath approximate to one another, so as to form a narrow 

 fissure ; the bent neck onlv of the archegonium projects out 



8 



