2 Development of the Fern Leaf 



the sum of the stages of development of the form and venation of 

 the leaf in each species, than with knowledge of isolated stages, 

 however advanced, alone. This is especially true if, as there 

 seems reason to believe,* traces of each of these plants' descent 

 are to be seen in phases of the plant's leaf during its develop- 

 ment. 



Most fern students, however, cannot easily obtain more than 

 isolated and, usually, mature stages. It seems, then, worth while 

 to ascertain, if possible, both the various modes of development 

 of form and venation in fern leaves, and the various effects pro- 

 duced by these in the leaves, in order that the modes of this 

 development in any species' leaf may be recognized from isolated 

 stages of the leaf, and a working knowledge of the missing stages 

 thus gained. 



It is proposed to outline in this chapter the different modes of 

 this development, as shown in the fern species of the northeastern 

 United States, and to point out in succeeding chapters various 

 effects produced by these in the leaves of certain of the species. 

 Such species have been included as serve to represent a wide 

 diversity of effects. While the account contained in this chapter 

 is based principally on specimens of the species of the northeastern 

 States, it has been confirmed on examination of very many speci- 

 mens of other species. 



The development of the fern species' leaf from the first to 

 the adult stage is exemplified, as fern students know, not in a 

 single leaf, but in a series of leaves. This series is borne by the 

 fern-plant, which is technically known as the sporophyte. The 

 leaves of the series, which begins with the first leaf produced by 



* See p. 8. 



