PROCEEDINGS OF SOCIETIES, 377 



Botanical Society of Edin burgh. — November 2th. — Alexander 

 Bucliaii, M.A., President, iti the chair. The President delivered an in- 

 augural address, of which the following is an abstract : — 



I propose in this address to make some remarks on climate and wea- 

 ther relative to the geographical distribution of plants, havini>- recently 

 completed certain inquiries regarding prevailing winds and rainfall which 

 are so intimately connected with the subject. In 1847, De Can telle made 

 some researches into the causes which limit vegetable species t )wards the 

 north in Europe and similar regions, and arrived at the conclusion that 

 every species having its northern limit in central or northern Europe ad- 

 vances as tar as it finds a certain fixed amount of heat, calculated from 

 that day of the year when " a certain mean temperature commences to the 

 day when that mean terminates." This law he applied with great inge- 

 nuity, in explanation of the northern limit of Ali/ssiim calyclnaai, Euohij- 

 mus europcsan, and Blantlius Carihnsianornm. It is evident that this law 

 can be best tested by applying it to the limits of wheat, barley, the vine, 

 and other cultivated species, since owing to the care taken of them by 

 man in their cultivation, it' may be consideretl that it is climalic condi- 

 tions alone which set the limits to their distribution. According to 

 Boussingault, wheat requires 8248° F. from the time it begins to grow 

 in spring for the proper ripening of the crop.; and moreover, this heat 

 must be so distributed as to secure a mean temperature of 58° during the 

 period when the seed is ripening. This statement referred to the conti- 

 nent of Europe, to which his researches were confined. But we have 

 found in Scotland that a mean temperature of 56° with the average 

 amount of rain and sunshine, is sufficient to ripen wheat properly. Not 

 only so, but the crops of 1864 ripened well with a temperature as low as 

 54"4 ; in this year, however, the sunshine was much above the average, 

 and the mean of the day temperatures was high. Now whatever be the 

 cause, whether the longer day in Scotland, or the clear sky, or bjth com- 

 bined, which brings about the above results, it is clear that in co isidering 

 the infiuence of temperature on the ripening of plants, it is not merelv 

 mean temperature, but the manner in which this vital element is par- 

 titioned during the twenty-four hours which must be taken into aci'ount. 

 Now what most influences the mode in which temperature is dislribntcd 

 during the day is the amount of cloud and moisture in the atmosphere, to 

 a knowledge of which the rainfall through the months of the year may be 

 regarded as furnishing the best available key. Indeixl, so great is the 

 direct and indirect infiuence of moisture on plants, that we shall not be 

 far wrong in supposing it to be co-ordinate with that of temp 'ratiire. 

 De Candolle's researches applied to a region where the climates are de- 

 termined rather by variations of temperature than of moisture. Not the 

 least valuable of the results he arrived at in ap])lying the law to other 

 regions is this, viz. " On the borders of the Mediterranean St^a, the limits 

 appeared so often determined by the humidity, or by causes still unknown, 

 that the operations of temperature always eluded my calculations." In 

 the climates of this region the rainfall plays a conspicuous part, and 

 hence, as was to have been expected, an assumed climatic limit to species 

 which did not include the rainfall, turned out to be inapplicable to the 

 facts of distribution. Again, perennial species, especially trees and shrubs, 

 are in many cases arrested, or limited, by the absolutely lowest tempera- 

 tures that occur. The great frost of Christmas 1860 brought us very 



