DEVELOPMENT OF PLANTS 289 



goes on very slowly within the archegonium where it lives as a 

 parasite for a long time. Eventually the root ruptures the arche- 

 gonium or calyptra and comes in contact with the soil. The 

 cotyledon now grows upward and makes its appearance above 

 the ground as the first green leaf (Fig. 218, b). The sporophyte 

 thus becomes a self-supporting plant, although it probably remains 

 in part dependent upon the gametophyte for several years. At 

 this stage of development the young sporophyte is a very simple 

 type of fern, but gradually more efficient roots are developed and 

 each year the stem sends up a larger and larger leaf until the 

 adult size is reached when the spore-bearing branch is formed 

 (Fig. 215), thus making possible again a new series of gameto- 

 phytes. 



(c) Comparison of the Adder Tongue Ferns zvith Preceding 

 Groups. The most noteworthy difference between these simple 

 ferns and the Bryophyta is the larpgr^teyelnprnent nf thfr Sporn- 

 phyte and_its final independence of the gametophvte. This is 

 doubtless due to the developmentof true ropts which made pos- 

 sible a continuous and abundant supply of the crude materials 

 from the soil. This change acted as a stimulus which promoted 

 variations in the sporophyte while the light and various climatic 

 factors also assisted to a very marked degree. Among the algae, 

 the gametophyte is the dominant generation, the sporophyte being 

 represented often by the gametospore. This is essentially the 

 relationship among the majority of the Hepaticae where the game- 

 tophyte performs all the work of food construction and the sporo- 

 phyte is a minute parasitic plant upon it. In Anthoceros and 

 the mosses, the sporophyte is longer lived and more highly organ- 

 ized, but the gametophyte is still the more important generation 

 as it performs the major portion of the work. Among the ferns, 

 this relationship and the distribution of labor is completely turned 

 about. The sporophyte becomes the larger plant and the prin- 

 cipal center of photosynthesis, while the gametophyte remains 

 small and gradually becomes very short lived. 



There is also to be noted the longer postponement in the for- 

 mation of the spores. 'In certain of the algae the gametospores 

 produce the spores directly on germinating while in Ricciocarpus 



20 



