34 PRACTICAL BOTANY. 



sporogonium maybe traced from the first divisions of the fertilised 

 ovum to the mature condition. 



For comparison with Marchantia the sporogonia of some 

 species of Jungermannia should also be examined : these grow 

 vertically upwards from the green thallus, and consist of a dark 

 spherical capsule, and a more or less elongated transparent 

 stalk, or seta, the base of which is surrounded by the calyptra- 

 When mature, the wall of the capsule splits into four, and the 

 flocculent mass of spores and elaters is set free. 



Cut median longitudinal sections of a sporogonium before the 

 stalk is fully elongated, and observe 



1. The parenchymatous structure of the stalk, which is 

 inserted by an enlarged foot in the tissue of the oophore. 



2. The capsule, consisting of a wall composed of two layers of 

 cells, which incloses the mass of spores and elaters. 



It will be well also to compare the sporogonium of Anthoceros, 

 noting the foliaceous irregularly-branched thallus, the upright, 

 elongated, and cylindrical sporogonia, which are inserted on the 

 upper surface of the thallus, and are surrounded at the base by a 

 sheath. The oldest sporogonia may have begun to split into two 

 equal halves from the apex downwards. 



Cut median longitudinal sections of a sporogonium of medium 

 age, and observe the enlarged foot with hair-like outgrowths pene- 

 trating the tissue of the oophore ; the zone of basifugal inter- 

 calary growth immediately above this ; the capsule above will 

 be seen to consist of a wall four or five layers of cells in thickness, 

 and having stomata ; a sporogenic layer, in which the division 

 of the cells into four may be easily recognised ; and a thin central 

 columella. Transverse sections will show that the wall is 

 thinner at two points than elsewhere, and it is here that the 

 rupture takes place when mature. 



