64 NOTICES OF BOOKS. 



12. The majority of the species enumerated in the list run into va- 

 rieties.* 



13- The seeds and fruits of the plants enumerated present no cha- 

 racters in common, and only 15 are distinguished by having mechanical 



aids to dispersion, 



A section is given to species inhabiting very circumscribed areas. 

 Of these, the majority of the best marked are insular, and the Is- 

 lands of St. Helena, Tristan d'Acunha, Madeira, and Juan Fernandez, 

 and the Gallapagos, present conspicuous examples. Of continental 

 European species, the most remarkable are Campanula excisa, Schl., 



Moretti 



Omphalodes 



ifolia 



phidaria Pyrenaica^ Benth. ; Wulfenia CarintJiiaca^ Jacq, 



A section treats of the mean area occupied by species, a subject far 

 too loose to admit of any accurate data being established from it ; it is 

 followed bv another, on the causes that determine the relative extent of 

 the areas occupied by species. Towards the solution of this question 

 little can be done beyond co-ordinating facts ; there has been much 

 false reasoning on it, as M, de CandoUe truly says : thus, that aquatic 

 plants occupy greater areas than terrestrial, is a fact that admits of no 

 solution in tlie present state of our knowledge ; it has been ascribed to 

 the fact of the temperature of water being more equable than that of 

 land ; but this is wholly unsatisfactory, for the same water-species in- 

 habits marshes in Italy and in Sweden, whilst different land-plants in- 

 habit equatorial regions that have a similar temperature and climate. 



The first volume terminates with observations on the causes that 

 determine the extension or non-extension of species; on the mode of 

 discriminating between botanical or physiological and geographical 

 causes, and between modern or existing and anterior or suppressed 

 causes of extension ; and lastly, with an elaborate application of these 

 principles to known facts. 



{To he continued.) 



* Perhaps the most significant ohservation in this valuahle Wor^c, and one 

 that is pregnant with results, when philosophically applied to the whole question of 

 species. — Ed. J. B. 



