8 Development of the Fern Leaf 
in sand mixed with leaf-mold, on a bank near the sea,on Shelter 
Island, New York; in the series borne by plants growing on 
rocks, on an exposed hillside, in central Vermont; and in the 
series borne by plants raised in mixed soil in flower-pots kept 
under glass in a greenhouse. 
There is, however, one hypothesis which offers a rational 
explanation of such changes; namely, that in the species’ leaf 
during its development are indicated characters that the leaves 
of the plant’s ancestry possessed. That is what we should expect 
to be true if we accept as true the alleged fact that in other living 
things traces of the individual’s ancestry are to be seen in 
changes which take place in the individual during its develop- 
ment from the first to the adult stage. 
The fact that, in the case of ferns, the changes in the leaf, 
which is a part of the fern individual, are exemplified in a series 
of successive ephemeral leaves rather than in one persistent leaf, 
need not militate against this hypothesis; which finds support in 
such facts as the following, difficult to account for on any 
other. 
(t) In some species peculiarities are present in the early 
stages of the leaf which disappear in the later stages: in some 
peculiarities are absent in the first stages which appear and are 
gradually intensified in the later. For example, in the early 
stages of the leaf of Nephrolepis exaltata, according to Mr. A. A. 
Eaton,* the leaf’s pinne are crisped and bristly at margin with 
excurrent nerves, but lose these characters as the leaf becomes 
mature. In the first stages of the leaf of Polystichum acrostichoides 
spinulose points on the leaf’s margin are absent, but in later 
* See Fern Bull. 11: 47, 1903. 
