526 



HUTCHINSON'S POPULAR BOTANY 



sporange is closed by an epiphragm supported on a central pillar, the 

 columel, which rises from the base of the sporange. The wall of the 

 sporange contracting in dry weather brings the epiphragm half-way up 

 the peristome, thus allowing the spores to sift out between the teeth. In 

 damp weather, with the elongation of the sporange, the epiphragm again 

 comes to the base of the peristome and the orifices are closed. In the Order 

 Phascacese the sporange does not dehisce at all, and the spores are only 



liberated by the decay of the walls. In 

 Andreaceae, again, there is no opercule, 

 but four or eight slits appear in the spor- 

 ange wall, from below the summit to near 

 the base. In addition to this sexual pro- 

 cess, Mosses may be produced vegeta- 

 tively by throwing off little buds, which 

 root and develop into perfect plants. In 

 some of our native species this is the only 

 method of reproduction, the sporangia 

 never being produced. 



In the Liverworts and Scale Mosses 

 we find two distinct types a more or less 

 flat green scale like a large fern pro- 

 thallium, and a delicate plant with a well- 

 marked differentiation into stem and 

 leaves. Species that conform to the first 

 type are known as Thalloid Hepatics ; 

 such as answer the second description are 

 Foliose Hepatics. Both forms are entirely 

 cellular, and are attached to the soil by 

 root-hairs. The process of reproduction 

 is similar to what we have seen in the 

 Mosses, in that the spore gives rise to a 

 protoneme from which the sexual gener- 

 ation is developed. The mode of bearing 

 the sexual organs differs in various orders 

 and genera. They may be produced from 

 the growing point of the main stem or 

 branches of the Foliose forms ; in the substance or on the upper surface of 

 the Thalloid forms, and in Marchantiacese on a special stalked outgrowth 

 of the thallus, and known as the antheridiophore or the archegoniophore, 

 according to sex (figs. 665, 666). Both organs may be produced by one 

 plant (monoecious}, or they may be on separate plants (dioecious). These 

 sexual organs originate in little swellings, which afterwards are seated 

 each on its own little foot-stalk. The antherid splits irregularly and sets 

 free a number of cells, each containing a spirally coiled, ciliated antherozoid. 



FIG. 670. LIVERWORT (Marchantia 

 polymorpha). 



An archegonium. 



