68 RE VIE WS. 



known facts and i)i-inciples towards the more complex, li3'po- 

 thetical and obscure), we will copy the titles of the chapters, 

 twenty-seven in number ; which are arranged in four books, 

 and subdivided into articles, and these again into sections, to 

 such an extent as to fill eight closely printed pages with the 

 bare enumeration. Indeed, this repeated subdivision gives a 

 rigid and rather tedious aspect to some parts of the work, and 

 involves occasional repetitions ; but it would not be easy to 

 collocate well and clearly so vast an amount of material in 

 any better way. 



The First Book is occupied with some preliminary consid- 

 erations upon the way in which temperature, light, and mois- 

 ture act upon plants. Its three chapters treat of the relations 

 of jilants to surrounding physical conditions, and especially to 

 heat and light ; and contain the author's happy distinction be- 

 tween the temperatures actually operative in vegetation, and 

 those which (being below the freezing point, etc.) are alto- 

 gether null for vegetation, and ought to be eliminated from 

 the tables of mean temperature, when these are viewed in 

 relation to the northern and southern geographical range of 

 species. 



The Second Book is devoted to Geographical Botany, or 

 the study of species, genera, and families, from a geographical 

 point of view. Chapter iv. relates to the limitation of species 

 upon plains and upon mountains, and the probable causes of 

 their actual limits, applied both to spontaneous and cultivated 

 plants ; and there is good endeavor to show that the northern 

 limit of species is fixed rather by the sum of heat available for 

 vegetation during the growing season, than by the mean tem- 

 perature of the year. Chapter v. treats of the shape of the 

 area occupied by a species, a very curious point ; and it seems 

 that the area of species inclines to be circular or elliptical. 

 Chapter vi. treats of the associations or disjunction of the in- 

 dividuals of a species in its area. Chapter vii. treats of the 

 area of species as to extent of surface, considered as to the 

 families they belong to, as to stations, as to size and duration 

 of tlie jdant, and as to the character of the fruit and seed, 

 whether affording facilities to dispersion or not. Chapter viii. 



