S6 ROMANCE OF LOW LIFE AMONGST PLANTS. 



many new species have been enumerated, so that we 

 may fairly consider that, during nearly a quarter of a 

 century, the number has been raised to at least eight 

 thousand species, or probably about equal to that of 

 the mosses. Very few of the lichens are of any 

 economic value, since the advance in chemistry has 

 superseded the dye-lichens, to a very great extent, by 

 artificial products. As articles of food they were 

 always miserable substitutes, and in medicine more 

 fanciful than of real value. 



One important feature may be noted in which 

 lichens differ greatly from other cryptogamic forms, 

 and it is a difference of great importance to remember. 

 It is thus stated by Dr. Lauder Lindsay : " Lichens 

 are perennial ; they grow very slowly, but they attain 

 an extreme age. Some species growing on the 

 primitive rocks of the highest mountain ranges in 

 ihc world, are estimated to have attained an age of 

 at least a thousand years ; and one author mentions, 

 after the lapse of half a century, having observed the 

 same specimen of Sticta pulnionaria on the same spot 

 of the same tree." 



Efforts have been made, on more than one occa- 

 sion, to demonstrate that the growth of lichens upon 

 trees is injurious to the tree. This appears to be 

 controverted by one small fact. Pharmacists are 

 aware that the most valuable kinds of cinchona bark, 

 as for instance " Crown bark," are habitually covered 

 with lichens, and that this covering favours the 

 development of the alkaloids. The inferior kinds oi 

 bark are not inhabited by lichens. Acting upon 

 this suggestion, a practice has arisen in cinchona 



