FROM AN OLD STANDPOEN'T. 



189 



the great groups have undergone. Hei-e, for instance, might be 

 placed the genesis of the rest-period of the seed, which would 

 then he regarded as an adaptation to seasonal variation, or iu 

 other words, as a result of the development of the seasons (see 

 <?hapter xxxi of my book on PI ant -Dispersal). Here also might 

 belong the transition from the dehiscent to the indeliiscent seed- 

 vessel or spore-case, wliich, as observed by Professor F. W. 

 Oliver (address Botau. Sect, Brit. Assoc., 1906), is to be found 

 in every group of plants, whether of cryptogams or of phanero- 

 gams. Behind the interesting fact that the capside is older than 

 the berry may lie many chapters in the climatic history of our 

 globe. 



The response to the divcrsijication of climate, or to the 

 conditions determined by it, would be foimd iu the successive 

 diflerentiation of tribes, genera, and species, the tribes reflecting 

 the first great changes influencing large portions of the globe, 

 the genera corresponding to subsequent changes affecting 

 considerable sections of the tribal areas, and the species to still 

 later changes affecting limited localities within the generic 

 area5. Every plant thus bears within it the double impress of 

 the changes in climatic conditions, or in other words, two sets 

 of characters, one very ancient, which it possesses in common 

 with all other plants, the result of such general changes as the 

 lowering of the earth's temperature, the decrease of humidity, 

 the increase of light, and the development of the seasons, the 

 other, more recent, which it shares with a relatively small 

 number of plants belonging to its own association, the immedi- 

 ate result of locality. It may be that the floral oi-gans have 

 mainly responded to the secular changes of climate that affected 

 the whole globe, whilst the vegetative organs chiefly reflect the 

 influence of the hxalised or differentiating climatic changes. 



It will be surticient now to refer briefly to the general desic- 

 aition of the globe, one of the most conspicuous in the secular 

 alterations of climate that have influenced plant-development, 

 reserWng the diversification of climate for consideration with 

 the differentiation of floras with which it is so intimately 

 connected. 



27i€ Jisiecaiion of the [jiuht. — The conception of a desiccating 

 world is by no means novel amongst men of science. We find 

 it most recently alluded to in the pages of Suess,* where we 

 learn that dui-ing the seventeenth and eighteenth centuries it 

 was held by philosophers and naturahsts. more particularly by 



Boi J ntlt'iz der Erde French edition, tome ii, chap. L 



