31G 



sophical character. In lieu of other subjects a discussion 

 irregular in its mode was allowed. 



Some allusions being made in the course of the meeting to 

 the appearance of lichens on the stones in the adjoining grave- 

 yard, the Chair occupied some time in explaining their ori- 

 gin, mode of increase and uses in the vegetable kingdom. 

 He also observed that these little and obscure plants had 

 certain geographical limits and a fixed distribution, seeming- 

 ly dependent upon climatic conditions ; that there were spe- 

 cies which affected maritime exposures, and were not found 

 inland, of which the most common yellow foliacious species, 

 the Physcia parietina was an instance. Next to this, the 

 Physcia chrysophthalma was of rare occurrence as it was 

 traced inland, and though extremely common in this vicini- 

 ty for instance, yet he had searched for it in vain at no great- 

 er distance than about Lowell in Middlesex county. Again, 

 the Placodium murorum, a cosmopolitan species, abounded 

 on our maritime rocks and seemed best suited to mark the 

 line of growth between the terrestial and ocean vegetation ; 

 while Placodium elegans also growing in the closest prox- 

 imity, re-appeared further inland and occurred upon the 

 rocks exposed to the winds and waves, which were com- 

 mingled upon the shores of the lakes. Certain species too 

 affected certain wrought stones almost exclusively, and the 

 marble slab and the sandstone monument in the graveyard 

 each, had its particular lichen growth. These were singu- 

 larities not wholly explicable upon any known theory. All 

 these obscure plants subserve particular functions in nature ; 

 and none can be regarded as useless in its economy. A 

 similar law of distribution affects elevations above the sea- 

 level, and mountain altitudes agree often in its lichens with 

 distinct parallels of latitude, those of the high northern re- 

 gions of the globe being found in alpine heights of our New- 

 England mountain chains. 



