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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 
