48 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



or virtually constitute the vegetation over considerable areas of the 

 drier habitats, they are also found as minor — but sometimes con- 

 spicuous — constituents of the vegetation in temperate and even 

 tropical regions. They are especially significant as pioneer colonists 

 on bare areas, and in boreal regions where they afford much of the 

 winter food of wild Reindeer and Caribou. Economically they are 

 important chiefly in the feeding of domesticated Reindeer, on which 



,. : n^f^-^r?^^^^ 



C D 



Fig. 12. — Various forms of Lichens (Lichenes). A, Ihnea baibata, a branched 

 epiphytic type (x i); B, Haematomma puniceuiii, a crustaceous type ( s i); C, 

 Cladonia reiticillnta, a terrestrial fruticose type ( ■ A); D, Lubayia piibnuiiaria, 



a foHose type ( ■: f ). 



