REPRODUCTION IN PLANTS 103 



spores and is the sporophyte. The gametophyte arises 

 asexually, but is itself sexual; the sporophyte arises sexually 

 but is itself asexual. The dominant generation from the 

 viewpoint of both structure and nutrition the plant one 

 thinks of as a 'moss' is the gametophyte. 



2. The Fern 



The common Ferns comprise the largest group of one of the 

 major divisions of the plant kingdom known as the PTERIDO- 

 PHYTA. Although the forms of different species are remark- 

 ably varied, the ensemble of characters and in particular 

 the foliage is quite distinctive, so that one would recognize 

 practically any member of the group as a 'fern.' The stems 

 may be short and close to the ground, or upright as in the 

 Tree Ferns, though creeping and underground stems 

 (rhizomes) are more common. The leaves, known as FRONDS, 

 either arise in clusters from the tip of the stem (Tree Ferns), 

 or are distributed along the creeping and underground stems. 

 Roots bring the stem into intimate contact with the food 

 materials of the soil, though rhizomes function to a certain 

 extent as roots. An examination of the cellular structure of 

 a common Fern, such as Aspidium marginale, shows that it 

 is much more complex than a Moss, the tissues of stem and 

 leaves being essentially like those we have seen in the Flower- 

 ing Plants, and accordingly Ferns and Flowering Plants are 

 frequently referred to as vascular plants. 



The leafy fern plant bears, on certain of its fronds, repro- 

 ductive organs which are sporangia. These, of course, pro- 

 duce spores and therefore the plant commonly recognized as 

 a Fern is a sporophyte. The spores when ripe are liberated 

 from the sporangia and fall to the ground, where they germi- 

 nate. From the spore arises a tiny body, about a quarter of 

 an inch in diameter, called a PROTHALLUS, which is essentially 



