26 Development of the Fern Leaf 



subdivide, and upon the extent to which this subdivision is car- 

 ried, in the course of the leaf's development. 



Instances sometimes occur in which some part of a species' 

 leaf that normally is undivided becomes subdivided into seg- 

 ments, and one, or repeated, series of segments may arise from 

 these. Such development of the leaf may be characterized as 

 monstrous. It sometimes produces most beautiful crested and 

 ruffled effects in the leaf. Many so-called "varieties" are based 

 upon leaves that are only monstrously developed. 



Monstrous development may occur in any part of a leaf, and 

 in one leaf only, or in more or in all of a plant's leaves. When 

 it occurs in more than one of a plant's leaves, it often varies in 

 degree in the different leaves, although it may affect similar parts 

 in these leaves. 



When the monstrously developed leaf is fertile, monstrous 

 development similar to that which appears in it often appears in 

 the leaves of any plants which may spring from its spores. 



It is sometimes difficult to distinguish between monstrous de- 

 velopment and normal development carried further than usual. 

 The latter, however, is to be looked for in especially luxuriant, 

 mature, fertile plants, and produces effects that appear the logical 

 sequel to all that has gone before in the way of leaf -development ; 

 while the former, due to unknown causes, is often correlated with 

 partial or complete sterility of the leaf, often produces freakish 

 effects, and is apt to be visible from the first appearance of leaves 

 on the plant. 



