284 PRACTICAL COURSE IN BOTANY 
AV 
SY 
EN 
= 
Fias. 419, 420. — A resurrection fern: 419, in dry weather ; 420, after a shower. 
to have become decomposed and mixed with humus, and the 
vegetation that first populates them has to do the pioneer 
work of disintegrating and impregnating the substratum with 
