38 



THE HABIT AND THE HABITAT OF FERNS 



[CH. 



It may be shown experimentally that the leaves of Ferns, like those of 

 Flowering Plants, react directly to the conditions under which they develop. 

 The effect of exposure to full sun in relatively dry surroundings is seen in 

 Fig. 45, (i), for Dryoptejas, and the effect of growth under deep shade in 



Fig. 43. Climbing Xa^i o{ Lygodium palniatiini, from N. Carolina. 

 {\ size. After Christ.) 



Fig. 45, (ii). The average measurements for a number of cases showed that 

 the area of the shade-form may be practically double that of the sun-form. 

 But the sun-leaves are more robust in structure, and give a higher spore- 

 output from their sori. Similar results were obtained by experiment from 



