174 M. C. COOKE ON THE DUAL-LICHEN HYPOTHESIS. 



an age of at least a thousand years ; and one author mentions, after 

 the lapse of nearly half a century, having observed the same sjDeci- 

 men of Sticto pulmonaria on the same spot of the same tree.* 



On the other hand, the Discomycetous Fungi are annual, very 

 short-lived, their whole existence being limited to a few weeks, 

 rapid in growth, and rapid in decay, not a trace of some species 

 remaining after a few days. 



Lichens will exist under conditions of aridity which no other 

 vegetables could support. Some are peculiar to calcareous rocks, 

 a few are found on arenaceous rocks, many are common on the 

 granitoid series, including micaceous, gneissic, granitic, and quartz- 

 ose rocks, and Lee idea geographica is frequent on the purest and 

 smoothest quartz. 



Fungi, on the contrary, must have moisture for their very exist- 

 ence sake ; are mostly found in damp and shaded situations, and 

 could never exist under the conditions just enumerated for Lichens. 



The highest mountains, beyond the snow-line, at 16,000 feet 

 on Chimborazo, the extreme limits of vegetation at the North and 

 South Pole are occupied by Lichens. Dr. Hooker found 

 three species of Discomycetes in the Falkland Islands, to 116 

 Lichens. The Reindeer Moss and species of Umbilicaria flourish 

 amongst the snow. On the other hand, frost and snow are fatal 

 to Discomycetous Fungi, which disappear long before the snow- 

 line is reached on mountains, and even before phanerogamic vege- 

 tation in the direction of the Polar regions. Of all plants, Lichens 

 support extreme cold most successfully, whilst Fungi succumb at 

 the approach of frost. 



Lichens which grow upon the bark of trees may be seen flourish- 

 ing in profusion during the life and vigour of the tree. It has been 

 affirmed that the portions of Cinchona Bark which have been covered 

 with Lichens during growth abound in the Alkaloids, on which 

 their medicinal use depends, j whereas the portions attacked by 



* Dr. Lauder Lindsay, " Lichens," p. 52. 



f Pharmacologists are aware that the most valuable lands of Cinchona 

 Bark, as, for instance, the " Crown Bark," are habitually covered with 

 Lichens, and that this covering favours the development of the Alkaloids. 

 Regarding this fact, the late Mr. Mclvor, of Ootacamund, introduced the 

 plan of covering the growing branches of Cinchona plants with moss, 

 and the bark thus mossed produced a larger percentage of Alkaloids than 

 the naked bark. The operation may be purely mechanical, such as 

 obstructing the light. However this may be, certainly no injury is 

 inflicted, but benefit is conferred by the growing lichens. 



