HEP A TIC^. 



351 



and longitudinal walls are formed in the external cells of the ventral portion, and 

 a wall consisting of one or two layers of cells is produced ; similarly, the wall of the 

 neck, which consists of five or six longitudinal rows of cells, is formed by the 

 transverse division of the peripheral cells of the upper tier. The primary stigmatic 

 cell divides into the five or six stigmatic cells of the neck. The cell originally 

 constituting the pedicel has also undergone both longitudinal and transverse divi- 

 sions. Whilst the oosphere is being formed, the walls of the canal-cells of the neck 

 and the transverse septum beneath the ventral canal-cell become converted into 

 mucilage, the swelling up of which forces the protoplasm of the canal-cells out 

 through the opened apex of the neck. (See Figs 236 and 256.) 



(2) The Asexual Generation, the Sporogonium, arises and is entirely formed 

 within the growing ventral portion of the archegonium, which from this time is 

 termed the Calypira. The sporogonium does not anywhere unite in its growth 

 with the surrounding tissue of the vegetative structure of the sexual generation, 

 even when its seta penetrates into it. 



The external form and internal structure of the sporogonium are very different 

 in the diff"erent groups. In the Anthoceroteae it is when mature an elongated two- 

 valved pod projecting from the thallus. In the Riccieae it is a thin-walled ball 

 entirely filled with spores, and, together with the calyptra, depressed in the thallus. 

 In the Marchantieae it is a shortly-stalked ball enclosing elaters as well as spores, 

 and, after it has broken through the calyptra, bursting irregularly or opening by a 

 circular fissure and detaching an operculum. In the Jungermannieae it also ripens 

 within the calyptra, but breaks through it and appears as a ball borne upon a 

 long slender stalk; the wall consists, as in the Marchantieae and Riccieae, when 

 ripe, of a single layer of cells, but separates cross-wise into four lobes, to which 

 the elaters remain attached. The elaters are, as in the Marchantieae, long fusiform 

 cells, the delicate colourless outer layer of which is thickened within by from one 

 to three brown spiral bands. 



The sporogonium also originates in diff"erent ways. [The fertilised oosphere 

 is always first divided into two cells by a wall {basal wall) which, in the lower forms, 

 is inclined at an acute angle to the long axis of the archegonium, but in the Junger- 

 mannieae is at right angles to it. In Riccia the capsule is developed from the whole of 

 the oospore : in the Marchantieae and Anthoceroteae the short seta of the sporogonium 

 is developed from the lower or posterior {hypobasal cell) of these two cells, the 

 capsule being developed only from the upper or anterior {epibasal) cell : in the 

 Jungermannieae the capsule and the seta are developed from the upper (epibasal) 

 cell, the product of the development of the lower {hypobasal) cell being a small 

 filamentous appendage upon the dilated base (foot) of the seta. This first division is 

 followed by two others at right angles to it and to each other, so that the embryo 

 now consists of eight cells {octants). The subsequent divisions take place more 

 or less irregularly, but it appears that in the Jungermannieae the four epibasal 

 octants behave Hke apical cells, segments being continually cut off" horizontally, 

 but doubtless intercalary divisions also occur \] When the young sporogonium has 



* [On the embryology of the Hepaticse, see Hofmeister, loc. ciL; Kienitz-Gerloff, Bot. Zeitg. 

 '874-5; Leitgeb, Entw. d. Kapsel von Anthoceros, Sitzber. d. Wien. Akad. 1876, and loc. cii.J 



