PREFACE 



INNUMERABLE books have been written about ferns in their 

 mature stages of development, and many accounts exist of their 

 earliest stages, which end with the formation of the young fern- 

 plant, but very little respecting the intervening stages seems to 

 have been recorded. Although in these stages the fern-plant's 

 development takes place, including the leaf -development, the 

 literature of the subject consists of a few scattered papers only. 

 These papers, moreover, deal mostly with individual species, and 

 chiefly with the subject of cell-growth and kindred phenomena. 

 They scarcely touch upon the development of the form and ve- 

 nation of the leaf in each species, and in its individual aspect 

 only, without reference to its relation to such development in 

 other fern species. 



For these reasons, and in view of the important part that the 

 form and venation of the species' leaf play nowadays in the 

 classification of fern species, and of the fact that both often differ 

 widely in the early stages of the leaf from their characters in the 

 later, it is thought that to point out in this book the principal 

 features of the development of form and venation in fern leaves, 

 as seen in the species of the northeastern United States, will be 

 useful, and may serve to throw light upon such development in 

 fern species in general. 



In order to give a clearer understanding of the leaf-develop- 

 ment, in each chapter containing an account of this development 



