CHAPTER... 
DEVELOPMENT OF THE FERN LEAF 
Amonc the reasons for which study of the development of 
form and venation in fern leaves appears desirable, the following 
are conspicuous. 
In many cases, leaf characters supposedly specific are features 
of only comparatively late stages of development of the species’ 
leaf. As might be expected from that fact, this development 
sometimes, by exceeding its usual limits, partly or wholly ob- 
literates such characters. In any delimitation of fern species, it 
is thus necessary to take into consideration the leaf-development 
of each species. In order to do this, and sometimes also in order 
to distinguish between what is due to this development and what 
is due to subspecific or other variation, it is necessary to know 
something of the modes of development of the form and venation 
of the leaf of each species in question. Instances are not wanting 
in which failure to understand the phenomena of such develop- 
ment has misled fern students into interpreting different stages 
of one species’ leaf as leaves of different species or of different 
varieties of the same species. 
It is evident that in many cases a clearer conception of the 
genetic affinities of fern species can be formed with knowledge of 
_ GARDED 
