INTRODUCTION TO THE FLORA. 233 



Stand its ground in them and prosper. To designate the 

 different kinds of locahty we may employ a series of adjectives 

 such as sylvestral, pratal, pascual, ericetal, uhginal, agrestal, and 

 say that Drosera rotundifolia is a uhginal, Capsella Imrsa-pasioris 

 an agrestal, and Hieraciimi tridentatiiin a sylvestral plant. 

 These terms answer the purpose of conveying, in connection 

 with a species, the idea of a certain definite association of 

 physical conditions ; but we must bear in mind when we employ 

 them and read them that they do not, and from the nature of 

 the case cannot, cover and give expression to much in regard to 

 conditions of station which has an important bearing upon distri- 

 bution, and that, for the most part, they deal only with such of 

 what may be called the factors of station as are to be met with 

 in most districts of an ordinary character, ^^^hat I mean by 

 this is, that in most tracts of country of any considerable extent 

 there are to be found woods, hedges, meadows, pastures, bogs, 

 heaths, and cultivated fields, the woods producing character- 

 istically sylvestral species, the hedgerows characteristically septal 

 species, the meadows and pastures characteristically pratal and 

 pascual plants, and so on through the series. In a limited tract 

 of country the most prominent facts of species-distribution, so 

 far as we can trace any connection with physical agencies at all, 

 are plainly to be a.ssociatcd with differences between the condition 

 of different parts of its surface such as are expressed by these 

 adjectives. But when we come to speak ofthe physical conditions 

 and agencies which interfere to modify or regulate the distribu- 

 tion of species over a more extensive area, these adjectives 

 answer our purpose no longer, and we are compelled to leave 

 them Ijehind, 



The Injluence of Temperature upon the Distributioji of Species. — 

 And then comes the question what are the factors that we can 

 deal with which the terms wc have alluded to do not cover which 

 have a bearing upon the distribution of species on a grand scale. 

 Of these, Temperature is plainly the most important, and the 

 difference in the way in which in different cases its influence is 



July I&S.y 



