ECO LOG Y. 



leaves which enable them to endure long periods of drought. 

 These plants have either succulent leaves like certain of the 

 stone-crops (sedum), or small thick leaves which are closely 

 overlapped as in the Saxifraga oppositifolia. 



Few of us, unfortunately, can make the trip to the arctic 

 regions to study these interesting plants which play such an 



Fig. 262. 

 Rock lichen (umbilicaria) from Greenland. 



important role in the economy of nature. Rocky places, how- 

 ever, or loose stones are common nearer home. Observation 

 of their flora, and the means by which such plants derive nutri- 

 ment, store moisture, or protect themselves from drought, will 

 well repay outdoor excursions. 



