EXERCISE 100 

 THE FERN GAMETOPHYTE 



Materials. Fern gametophytes may be found in greenhouses 

 where ferns have been shedding spores. They are small, delicate, 

 heart-shaped green bodies not more than an eighth or a quarter of 

 an inch in diameter. (See textbooks for illustrations.) Fern gameto- 

 phytes are rarely found in the field even by experienced collectors. 

 The exercise may well be given as a demonstration with any but 

 the most advanced classes. 



Directions for work. The fern spores do not grow into plants 

 like the original. A spore when germinated produces a small 

 heart-shaped plant called the fern gametophyte (or the prothal- 

 lus). Examine a gametophyte, noting its characteristics. 



Consider its ability to secure food and water and its general 

 ability to succeed in the struggle for existence, using the same 

 outline as was used in the study of the moss plant. How does 

 the gametophyte generation of the fern compare with the gen- 

 eration of the fern just studied (sporophyte) in equipment for 

 successful competition with other plants ? 



The gametophyte produces sexual cells (gametes) which 

 unite to form sexual spores. From these the familiar spore- 

 bearing plant (Exercise 99) is produced. Young sporophytes 

 may be found attached to some of the gametophytes. 



In the life history of the fern, therefore, sporophyte and 

 gametophyte alternate. Is the gametophyte a weak or a 

 strong link in the life history? 



The leafy moss plant, with which you have been comparing 

 the fern, is a gametophyte; the spore case and stalk are the 

 sporophyte generation. The moss sporophyte is parasitic. Com- 

 paring the fern with the moss, has the sporophyte become more, 

 or less, important ? Has the gametophyte become more, or less, 

 important ? 



References 



BERGEN and CALDWELL. Practical Botany, pp. 282-286. 

 BERGEN and CALDWELL. Introduction to Botany, p. 274. 



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