NOTICES OF BOOKS, 63 



4. The plants characteristic of different localities bear a very diflferent 

 proportion to one another in the list, to what they do to the whole 

 Phaenogamic vegetation. 



6. The aquatic or subaquatic appear to have been dispersed widely, 

 quite independently of the agency of man. 



6. Not one tree or bush appears on the list;* the Thymus SerpylUm 

 is the only approach to a woody plant. 



7. The list contains 47 annuals, 3 biennials, and 66 perennial-rooted 

 plants. 



8. The great extension of continent towards the north of our hemi- 

 sphere powerfully influences the distribution of many species; no less 

 than 108 of the 117 entirely or chiefly occupy the temperate or cold 

 latitudes of the northern hemisphere. 



9. The species in the list may be supposed to have spread without 

 difficulty from station to station on the continents: but it is worthv of 

 remark, that every species which is widely diffused over both conti- 

 nents, inhabits also the intervening islands, under the same latitude. 

 Hence it follows that the oceans were no greater obstacles to the dis- 

 persion of the plants in question, than the land was, or that the dis- 

 persion took place at a period when the islands were nearer the conti- 

 nents, or formed part of them ; or, lastly, that the same species origi- 

 nated in more than one locality. 



10. The species most widely diffused belong generally to families 

 which have been already noticed in this Work, as containing species 

 that occupy large areas : from this M. de Candolle adds a corollary, 

 that when a famQy contains one or more species of unusually extended 

 I'ange, most of the other species of that family may be assumed to oc- 

 cupy considerable areas. 



11- The proportion of Dicotyledons to Monocotyledons in the list is 

 as .73 to 44 ; and as the whole number of known Dicotyledons to Mo- 

 nocotyledons is as 62 to 38, it follows that the species of Monocotyle- 

 dons occupy a gi'eater area than those of Dicotyledons. 



iQ a double ratio, for whilst the reduction of varieties to species and the additional 

 habitats increases the numerator, the former cause diminishes its denominator. — 



Ed. J. B. 



• When the tropical flora is better investigated, several decidedly bushy, if not 

 Jirboreous, plants, will no doubt have to be added, as perhaps Avicennia and other 

 coast-species, which at present have different names in the Old and New World.— 

 Kd. J. B. 



