180 A TEXT-BOOK OF BOTANY 



spore-case. It has a long slender stalk, which becomes 

 anchored in the stem of the leafy plant (Fig. 172); and the 

 stalk bears an elaborate and usually urn-shaped spore-case 

 full of spores (Fig. 173). This spore-case opens by means 

 of a lid, which drops off; and often at the mouth of the 

 urn thus opened there may be seen a set of delicate teeth 

 extending from the margin of the rim and meeting in the 

 center (Fig. 174). These teeth bend inward and outward 

 as they are dry or moist, and help discharge the spores. 

 It is evident that this spore-case with its anchored stalk is 

 the sporophyte generation in the life-history. 



When the spores fall in suitable situations they germi- 

 nate, and each one produces a green branching filament 

 that looks like one of the filamentous green Algae (Fig. 

 175). This branching filamentous growth spreads over the 

 substratum, and presently there appear upon it buds 

 (Fig. 175, B, b), each of which develops an erect leafy stem, 

 which is recognized as a new leafy moss plant, the form 

 with which this account of the life-history was begun. 



103. Alternation of generations. In the life-history just 

 given, it is evident that the prostrate green filament and 

 the erect leafy stems are two parts of the gametophyte; 

 for the leafy stems simply arise as erect branches from the 

 prostrate filament. It is strictly true, therefore, that the 

 so-called moss plant, the conspicuous part of the moss, is 

 a leafy branch of the gametophyte. These leafy branches 

 become independent of the filament by sending out rhizoids 

 into the substratum, so that it is only by actually germina- 

 ting the spores that the filaments are seen. Not only does 

 this branch bear leaves, and hence perform the chief work 

 of food manufacture, but it also bears the sex-organs. 



The sporophyte, on the other hand, is dependent upon 

 this leafy branch for its food-supply, and in that sense may 

 be said to be parasitic upon it. Its only work is to produce 

 spores; while the gametophyte does the chlorophyll work 



