468 APPENDIX. 



the underside at a point where the young roots also arise 

 and grow into the soil. The young plants, with the attached 

 prothallus, should be thinned out if they are crowded, and 

 they can be transplanted to a pot of soil, when they will 

 gradually grow into adult ferns. Before long the prothallus 

 itself withers and disappears. 



While the young fern plant was attached to the prothallus 

 it had a special absorbing organ, called the foot, which drew 

 food from the tissue of the cushion ; hence the embryo fern 

 consisted originally of four parts cotyledon, stem growing- 

 point, first root, and foot (Fig. 7). The stem grows very 

 slowly at first, as compared with the cotyledon and the 

 succeeding leaves; the first root is soon replaced by other 

 roots growing from the base of the young stem. The young 

 fern is rather exceptional among green plants in being able 

 to turn green even when kept in darkness, though it does not 

 thrive, but soon dies, unless it gets light. 



Alternation of Generations. It will be noticed that in 

 the life-history of the fern there are really two plants to be 

 considered. These are often spoken of as the two stages, or 

 generations, of the life cycle. The fern plant, by far the 

 larger and more conspicuous of the two, is called the sporo- 

 phyte, or spore-producing plant. The prothailus is called 

 the gametophyte, because it produces the gametes or germs. 



The life cycle of the fern, therefore, is a regular alternation 

 of sporophyte and gametophyte, and this is called the alter- 

 nation of generations. It will be noticed that both genera- 

 tions begin their development from a single cell, the young 

 sporophyte (fern plant) from a fertilised egg-cell, the game- 

 tophyte (prothallus) from a spore. The vegetative propa- 

 gation of the fern plant, in our type by the breaking off of 

 buds from the bases of the leaves, has no share in the 

 alternation of generations, except that it merely lengthens 

 out the life cycle. 



The Bracken, which agrees with the Male Fern in all 

 essential respects, differs a good deal from it in details. It 

 covers large areas, especially on heaths and commons, though 

 it sometimes grows in woods, where it may reach a height of 

 five feet, whilst in exposed places it is often stunted and 

 hardly over a foot high. The " frond," or leaf, the portion 

 of the plant which comes above ground, is often mistaken 



