58 NOTICES OF BOOKS. 



cated with artificial ones of all kinds, as with the history of nations, 

 their rise and decline, their intelligence, activity, and the abundance 

 or scarcity of food. The subject is divided into that of their Polar 

 and Equatorial limitation, and the species principally treated of are 

 ■Barley, Maize, the Vine, and Date. Of these the Barley appears 

 to give the most definite results, from the extent of the area over 

 which it is cultivated, and the exactitude of the data that have been 



observed regarding its limits. 



The chapter on the Limitation of Species is followed by concluding 

 remarks on the causes which limit species, whether at the level of the 



sea or upon mountains. 



Chapter 5. Form of the area inhabited by species ("Forme des ha- 

 bitations des especes**). — This is an exceedingly curious subject, hardly 

 capable of a very rigorous study ; some species occupy nearly circular 

 areas, others extend in one direction many times further than in another ; 

 the causes of these irregularities are to be found in the preceding chapter 

 on the limitations of species. Of 8495 species described in the three 

 last published volumes of De CandoUe's 'Prodromus,' it appears that 

 only 116 extend in one direction more than four limes as far as they 

 do in the other, whilst the greater number of species appear aggregated 

 in areas that approach a circle or ellipse in form. 



CJiapter 6. Aggregation and segregation of the individuals of a spe- 

 cies in difl'erent parts of the area it inhabits (" Repartition des individus 

 dans riiabitation de Tespece''). — The principal object of this chapter 

 is to sketch out the main features of the local distribution or Topo- 



w 



graphy of plants, or the local causes that determine their absence, pre- 

 sence, or prevalence in different localities. Of these some are very 

 evident, such as rocks, walls, hedges, brushwood, forest, prairies, sands, 

 turf, cultivation, waysides, farmyards, parasites and epiphytes, melting 

 snow, salt-marshes, fresh-water marshes, sea-water, fresh-water, warm 

 springs, etc. Of the less obvious influencing causes are the mineralo- 

 gical character of the soil, which seems to act chiefly through the 

 mechanical nature of the medium into which it disintegrates ; expo- 

 sure i the circumstance of the soil having long been occupied by a 

 species ; and the agency of the animal creation. This is followed by 

 an article on the very difl'erent localities afiected by the same species. 

 The comparative frequency of a species, or rather the comparative 

 abundance in which a species may exist, is next discussed, the means 



