No. V. 



On the Geographical Distribution of Plants. By C. Pick- 

 ering, M.D. — Read October I9th 1827. 



THE observations of travellers in every part of the globe, and 

 our greatly increased know^ledge of the species both of ve- 

 getables and animals, have of late years brought forward the 

 interesting subject of their geographical distribution. The 

 materials accumulated prior to the last half century w^ere few, 

 and insufficient to solve many questions which have since 

 yielded to the labours of naturalists. Much has been accom- 

 plished by Humboldt, Brown, Schouw and others — the sub- 

 ject is continually receiving increased attention, but it is uni- 

 formly rendered intricate by attempting to reduce under the 

 same laws both species and groups (as families, genera, &c.), 

 while it is evident that the local causes, which, in the one in- 

 stance, greatly influence their distribution, by no means affect 

 the other. In this essay, species and groups are examined 

 separately, the inquiry is directed more particularly to the 

 former, and their range is followed as a guide in the arrange- 

 ment here proposed. 



Solar heat is evidently the principle which puts in motion 

 the fluids of plants, and these vary in their relation to it, 

 some requiring a temperature that destroys others; conse- 

 quently, a plant being carried far north or south of its natural 



