32 



THE HABIT AND THE HABITAT OF FERNS 



[CH. 



and propagation during the favourable season. It seems probable from the 

 complex leaf-arrangement, and from the degrees of polyphylly seen in the 

 smaller species, that the monophyllous habit is an adaptive modification of 

 the usual basket-type, but with the successive leaves spread in their time 

 of expansion over a prolonged period. Biologically it compares with what 

 is seen in such Aroids as Arum niaciilaticui, or AmorphopJialhis. 



The creeping habit is in strong contrast to the upright. It results from 

 an elongation of the internodes with a consequent greater or less isolation 



Fig. 38. A small plant of Danaea alata, showing the lower part of 

 the axis vertical, the upper part obliquely horizontal. j'^ = stipules. 

 (I size. After Campbell.) 



of the leaves. Though the vertical and more compact shoot was probably 

 the primitive type, the creeping habit was certainly acquired early, for it is 

 seen in Metaclepsy drop sis duplex from the Culm. Its secondary origin in the 

 ontogeny of those primitive Ferns which have a vertical embryo may be 

 traced in Helminthostachys, Danaea, and Christensenia (Fig. 38), in all of which 

 the originally vertical sporeling falls over later to a creeping habit. Here 

 it seems to be a natural consequence of the heavy leaves weighing down a 

 weak stem. In the Leptosporangiate Ferns, however, where the embryo is 

 prone from the first, the upright habit which so many of them show in the 



