II MUSCINE^— HEPATIC^— MARCHANTI ALES S9 



The lacunar tissue is very much developed upon the 

 receptacles, as are to an especial degree the peculiar cylindrical 

 breathing pores. The formation of these begins in the same 

 way as the simple ones, being merely the original opening to 

 the aif-space. This seen from the surface shows an opening 

 with usually five or six cells surrounding it. Vertical sections 

 show that very soon the cells surrounding the pore become 

 deeper than their neighbours and project both above and below- 

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

 inclined walls b)' 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 cells of 

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

 Astroporse, 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 special- 

 ised of the Marchantieae, i. e., Marchantia, Preissia, 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 Sporophyte. 



The first divisions in the embryo of the Marchantiaceae and 

 Corsiniacese are the same as in the Ricciacese, but only the 

 upper part (capsule) of the sporogonium develops spores, 

 while the rest becomes the stalk and foot. The simplest form 

 of capsule is found in the genera Corsinia and Boschia, which 

 have been carefully studied by Leitgeb ((7), iv., pp. 45-47). 

 In these the embryo, instead of remaining globular as it does in 

 Riccia, elongates and very early becomes differentiated into a 

 nearly globular upper part, or capsule, and a usually narrower 

 basal portion, the foot (Fig. 22). 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 



