40 



THE HABIT AND THE HABITAT OF FERNS 



[CH. 



Comparison of these at large, when based upon average specimens from 

 normal stations, shows that Ferns of exposed habit have leaves of relatively 

 firm texture, wath narrower and highly divided segments, while Ferns of 

 shaded habit usually hav-e broader and less cut leaves of thinner texture. 

 Examples of shade-leaves are seen in Cliristensenia aesciilifolza, and in Hypo- 



Tig. 45. (i) Leaf of Dryopteris grown in the open with extreme exposure 

 to sun and wind, (ii) Similar leaf from the same garden grown pro- 

 tected from the wind, and in heavy shade. 



Fig. 46. Parts of the same leaf of the Bracken seen in 

 section, (i) is from a pinna exposed to full sun during 

 development. I'ii) is from a pinna developed in shade. 

 (After Boodle.) ( x 200.) 



derris Brozvnii. Ferns of shaded and moist habitat are often of still more 

 delicate texture than these, and usually have naked surfaces. The extreme 

 condition is that which is styled "filmy," in which the lateral wings of the 

 expanded lamina may be reduced to a single layer of pellucid cells. The 

 Hymenophyllaceae are the chief representatives of this habit, and they are 



