240 THE SIMPLEST LAND PLANTS 



they differ in certain details of structure. The sexual 

 organs, accompanied by hairs and surrounded by 

 leaves, which are sometimes coloured yellow or red, 

 are borne at the tips of upright shoots that have 

 stopped growing. 



The fertilised egg cell, like that of the Liverwort, 

 germinates in situ within the archegonium, and 

 the embryo grows into a sporogonium which, as in the 

 Liverwort, remains attached to the parent plant. The 

 Moss sporogonium, however, is of much more compli- 

 cated structure than that of the Liverwort. It has a 

 foot, stalk and spore capsule, but the stalk elongates 

 much earlier and possesses a central water-conducting 

 strand like that of the leafy stem. Surrounding this 

 there is sometimes a layer of elongated living cells 

 which conduct organic food to the developing spore 

 capsule. These are comparable in function with the 

 medullary cells of Fucus. The spore capsule itself is 

 quite an elaborate structure. Its wall consists of 

 several layers of cells containing chloroplasts and is 

 covered by an epidermis with stomata, possessing in 

 fact a structure like that of the leaf of a higher plant. 

 Thus the sporogonium, which, during development, is 

 supplied with organic food by the leafy parent plant, is 

 able when nearly mature to make some of its own food 

 from the carbon dioxide of the air and the water and 

 salts brought up from the leafy parent plant through 

 the foot and stalk. When the spores are ripe a lid 

 is detached from the top of the capsule, and distri- 

 bution of the spores is often assisted by the move- 

 ments of hygroscopic teeth set round the edge of the 

 opening, which thus perform the same function as the 

 elaters of the Liverwort capsule. The spores germi- 

 nate on damp soil to form an alga-like growth (proto- 



