120 Transactions. — Botany. 



the present and the pre-glacial flora, a connection is clearly 

 traceable. 



Whether we confine our attention to limited regions or 

 extend our observations over the earth, we find everywhere 

 that the main features of the vegetation are due to climatic 

 influences. Thus, in these islands we meet with contiguous 

 and sharply-defined districts clothed with dense bush or 

 associated grasses denoting difl'erences in the rainfall. These 

 features we see repeated on a grand scale in the vast forests 

 of the torrid zone and in the broad savannahs and prairies of 

 colder latitudes. 



Again, we have wide tracts, subject to long periods of 

 drought, tenanted almost exclusively by annuals, the adapta- 

 tion to climate being therein evident ; and in hot countries 

 where very dry and wet seasons alternate, we have the curious 

 phenomenon of heat-coma, displaying itself by the shedding of 

 leaves. 



Among climatic causes, then, it seems as if a reason for 

 the distribution of deciduous and evergreen trees must be 

 found ; but, no existing conditions tlirowing any light on the 

 matter, I have sought an explanation in such records as we 

 have of the past — witli what success I must let others, with 

 more knowledge, judge, for as I close these pages I am fully 

 sensible of having undertaken a task for which I was very 

 inadequately prepared. The solution of the question having 

 been, as far as I am aware, hitherto unattempted, if I merely 

 succeed in directing attention to it I shall consider I have done 

 well. 



