THE HIGHER CRYPTOGAMIA. 117 



ding portions are separated from the original cell-cavity by 

 transverse septa (PI. XV, fig. 13). By repeated transverse 

 divisions of the apical cells of the membranous sheath, pro- 

 duced by septa parallel to the free margin, the young 

 covering grows in length (PI. XV, fig. 14). Its fur- 

 ther development, viz., the transformation of the cylin- 

 drical shape into that of a distended pitcher (PI. XV, 

 fig. 15), corresponds to that of the covering of Fruttania 

 dilatata. 



Close under the arched upper surface of the receptacle 

 of Marchantia, including the outer surfaces of the 

 upward-growing shoots of the lateral margin, numerous air- 

 cavities are formed, even before the first appearance of 

 the archegonia. They are formed in the same manner as 

 the air-cavities of the stem. At the first appearance of the 

 air-cavity one epidermal cell only detaches itself from the 

 underlying tissue of the receptacle (PI. XVI, fig. 17, un- 

 derneath, to the right). By repeated transverse division 

 of the mural rows of cells lying between the air-cavities, 

 the lid of the cavity is carried rapidly upwards. This 

 epidermal cell, which closes the air-cavity, forms itself into 

 a stomate. It divides by a septum perpendicular to the 

 outer surface, as is the case in the first stage of the 

 stomata of the upper side of vegetative shoots ; both 

 daughter-cells then divide by a septum at right angles to 

 the one last formed (PI. XVI, fig. 17, in the middle). The 

 four cells part asunder at their edges of contact, and the 

 air-cavities come into connexion with the outward air. 

 The four cells of which the young stomate now consists 

 divide repeatedly by transverse septa. The first partitions 

 thus formed are parallel to the upper side of the receptacle ; 

 the later ones, which are produced in the upper and under 

 of the newly formed cells, are strongly inclined either towards 

 or away from the passage which traverses the axis of the 

 stomate. The apex of the organ protrudes above the upper 

 side of the receptacle in the form of a conical wart, open at 

 the apex ; the base lies deep down in the air-cavity 

 (PL XVI, fig. 7). The middle part of the canal, which 

 traverses the stomate, is strongly distended. In the mean 

 time the apical cells of the cellular walls, which separated 



