DEVELOPMENT OF PLANTS 319 



mains 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 de- 

 veloped 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 

 gametophytes. 



(c) Comparison of the Adder Tongue Ferns with Preceding 

 Groups. The most noteworthy difference between these simple 

 ferns and the Bryophyta is the larger development of the sporo- 

 phyte and its final independence of the gametophyte. This is 

 doubtless due to the development of true roots 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 

 gametophyte performs all the work of food construction and the 

 sporophyte is a minute parasitic plant upon it. In Anthoceros 

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

 organized, but the gametophyte is still the more important gen- 

 eration 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 

 principal center of photosynthesis, while the gametophyte re- 

 mains 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 

 a small mass of cells is first formed and certain of these cells 

 soon become spore mother cells. In Marchantia, a larger number 

 of cells are formed by the gametospore and the spore mother cells 

 originate after a few weeks in a definite region of the sporophyte. 

 These features are more noticeable in the Jungermaniales and 

 especially in the long-lived sporophyte of Anthoceros. Recall 



