XEROPHYTE SOCIETIES. 



195 



drouth it is very com- 

 mon for plants to 

 diminish the exposed 

 surface in a very de- 

 cided way. In such 

 cases there is what 

 may be called a peri- 

 odic surface decrease. 

 For example, annual 

 plants remarkably 

 diminish their ex- 

 posed surface at the 

 period of drouth by 

 being represented 

 only by well-pro- 

 tected seeds. The 

 whole exposed sur- 

 face of the plant, 

 root, stem, and leaves, 

 has disappeared, and 

 the seed preserves the 

 plant through the 

 drouth. 



Little less remark- 

 able is the so-called 

 geophilous habit. In 

 this case the whole of 

 the plant surface ex- 

 posed to the air dis- 

 appears, and only 

 underground parts, 

 such as bulbs, tubers, 

 etc., persist (see Figs. 

 45, 46, 66, 67, 68, 69, 

 70, 75, 144, 164tf, 

 164*). At the re- 



FIG. 164a. The bloo(lroot(Sanguinaria), showing 

 the subterranean rootstock sending leaves and 

 flower above the surface. After ATKINSON. 



