58 MOSSES AND FERNS chap. 



deeper than their neighbours and project both above and below 

 them. In these cells next arise (Fig. lO, A, B) a series of 

 inclined walls by which each of the original cells is transformed 

 into a row of several cells, and these rows together form a 

 curious barrel-shaped body surrounding the pore. The upper 

 cells converge and almost close the space above, and this is still 

 further diminished by the cuticle of the outer cell wall of the 

 uppermost cells growing beyond the cells and leaving simply 

 a very small central opening. The rows of cells also converge 

 below, and in Fimbriaria Californica the lowermost cells are 

 very much enlarged, and probably serve to close the cavity 

 completely at times, and act very much like the guard cell 

 of the stomata of vascular plants. In Leitgeb's group of the 

 Astroporae, the simple pores of the thallus have the radial 

 walls of the surrounding cells strongly thickened, so that the 

 pores seen from the surface appear star-shaped. The most 

 specialised of the MarchantiecE, i.e. Marchantia, Lunularia, etc., 

 have the cylindrical pores upon the vegetative part of the thallus 

 as well as upon the receptacle, but in the others they occur 

 only upon the latter. 



The Sporogonium 



The first divisions in the embryo of the Marchantiece are 

 the same as in the Ricciaceae, but only the upper part (capsule) 

 of the sporogonium develops spores, while the rest becomes the 

 stalk. The simplest form of capsule is found in the genera 

 Corsinia and Boschia, which have been carefully studied by 

 Leitgeb.-^ In these the embryo, instead of remaining globular 

 as it does in Riccia, elongates and very early becomes differenti- 

 ated into a nearly globular upper part, or capsule, and a usually 

 narrovv^er basal portion, the stalk (Fig. 20). In the capsule 

 at a very early period a single distinct layer of outer cells is 

 separated from the central group of cells, and forms the wall of 

 the capsule, which in Boschia at maturity develops upon the 

 inner cell walls thickened bars. Only a portion of the cells of 

 the central part produce spores ; the remainder do not divide 

 after the spore mother cells are formed, but remain either as 

 simple slightly elongated nourishing cells {Corsinia) or elaters 



{Boschia). 



1 Leitgeb (7), vol. iv. pp. 45-47- 



