THE HIGHER CRYPTOGAMIA. Ill 



the very young shoot, long before the completion of its 

 growth in thickness, air-cavities are formed just under 

 the upper surface, separated from it only by a single 

 layer of cells (PL XV, fig. 21; PL XVI, fig. 3). The 

 portions of tissue between the air-cavities form a network 

 of single rows of cells. As these cells continue to divide 

 by septa parallel to the surface of the stem, the lid 

 of the air-cavities is carried upwards. The base of 

 the cavities is quite flat. Lastly, after repeated pre- 

 vious bipartition of the cells of the base, by means of 

 vertical septa placed crosswise, the latter cells protrude 

 upwards (PL XV, fig. 21), and by repeated transverse 

 division are quickly transformed into the moniliform 

 chains of cells which, when the shoot is perfected, are 

 pressed closely, to one another and fill up the air-cavi- 

 ties. 



The epidermal cell which is situated over the middle 

 of each air-cavity separates by repeated bipartition into 

 four (Marchantia), six (Fegatella, PL XVI, fig. 4), or 

 more (Rebouillia) three-sided cells arranged in a circle. 

 In the centre of the circle the cells part from one 

 another; a polyhedral opening is formed, the circumfer- 

 ence of which, owing to the expansion in a tangential 

 direction of the surrounding cells, is often considerable, 

 and through which the air-cavities, in which air is secreted 

 at an early period, comes into contact with the atmo- 

 sphere. The first development of the stomata of the Mar- 

 chantieae is only distinguished from that of higher plants 

 by the fact that more than one bipartition of the mother- 

 cell precedes the opening of the commissure of the cells 

 which form the boundary of the opening. 



The cells, from four to eight in number, which sur- 

 round the stomata of the Marchantiese divide, during the 

 expansion of the stem to which they belong, by means 

 of septa parallel to the small side walls ; this often occurs 

 repeatedly, so that a hollow arch, with a perforated apex, 

 is formed over the middle point of the air-cavity. The 

 outer walls of the circular, wart-like protuberance of the 

 epidermis divide also by radial septa. 



The inflorescence of a Marchantia owes its origin to the 



