170 president's address. 



But on this subject, and on tlie annual growth of the stems of 

 Forest trees, we have by no means yet arrived at a full and per- 

 fect knowledge. 



After regarding those trees from different regions of the earth, 

 I am naturally led to congratulate the Botanists of our Society 

 on the publication of the most complete treatise on " Botanical 

 Geography" that has ever appeared. The valuable work which 

 I allude to is entitled " Geographic Botanique raisonnee,"* par 

 M. Aljjiionse de Candolle. Wahlenberg, Von Buch, Baron Hum- 

 boldt, Bamond, Robert Brown, Meyen, Dr. Hooker, H. Cottrell 

 Watson, Grisebach, Miquel, Lecoq, and a few others, have seve- 

 rally done much since the first publication, in 1822-3, on this 

 important subject by Professor Schouw, of Copenhagen. That 

 book, under the title of " Elements of a Universal Geography 

 of Plants," laid the foundation of our knowledge of this branch 

 of science ; and, as far as a general treatise went, it was very 

 useful, abounding in able views, and a full selection of facts and 

 authorities. 



The subject, as recently treated by M. de Candolle, is divided 

 mio four books. The first may be considered as Botanical Cli- 

 matology, or observations on the natural effects of climate; or, 

 miore strictly, on the action of temperature, of light, and of 

 moisture upon plants. The second book relates to Geographical 

 Botany; the third book to Botanical Geography; and the fourth 

 book contains some general conclusions. There is also an Ajypendix 

 setting forth certain investigations requisite for the advancement 

 of Botanical Geography, and the first volume has two geographi- 

 cal maps exhibiting the " Polar Limits" of several species. At 

 first sight, I must observe that it struck me that the divisions 

 of the second and third books were unnecessary ; for a full and 

 complete consideration of the one, must evidently include the 

 other; yet, on a further examination of these two books, I became 

 more satisfied with the author's distinctions and arrangements. 



The following result, with regard to the annual heat which 

 plants require, as deduced from De Candolle's own experiments, 



*The full title adds, " Ou Exposition des Faits Principaux et des Lois concernant la 

 Distribution GSographique des Plantes de I'epoque actuelle." — 2 Tom''- Geneve, 1855. 



