GEOGBAPHICAL AND GEOLOGICAL BOTANY. 



elsewhere once cleared and exposed to the influence of the sun, do not 

 become clothed again by forests such as they possessed formerly. Coni- 

 ferse and Amentaceous plants, which form the chief constituents of forests 

 in these regions, are Phanerogams of low organization. Their probable 

 antiquity, judging from their occurrence in masses in certain countries, 

 confirms the view that existing species are of unequal antiquity, and that 

 the older species are of lower type. 



The facts of existing Botanical Geography are in general clear 

 and concordant, if we suppose that the most ancient species of 

 Phanerogams comprise the majority of plants either aquatic or 

 loving moisture, then many northern and alpine plants and most 

 of the trees of our temperate regions. We may suppose at the 

 same time that the most recent species occur principally among 

 the plants of warm regions, among the Dicotyledons with an 

 inferior ovary and a gamopetalous corolla (such as Composite, 

 Dipsaceas, Campanulaceae, &c.) and among the other Phanerogams 

 with structure complicated in other respects (such as Orchidacese, 

 Palmaceaa, Apocynaceae, Asclepiadaceaa, Cucurbitaceae, Passinoracea?, 

 BegoniacesB, &c.). 



(The considerations stated in this Section are derived, with slight modi- 

 fications, from the ' Ge"ographie Botanique ' of Alph. De Candolle, a most 

 important general work on this subject, which should be studied by all 

 those who are interested in these questions. Lyell's 'Principles of 

 Geology,' vol. ii. Book iii., and Darwin's ' Origin of Species ' should also 

 be consulted, and for a brief summary Mr. Baker's ' Elementary Lessons 

 on Botanical Geography.') 



CHAPTER II. 

 BOTANICAL GEOGRAPHY. 



Sect. 1. DISTRIBUTION or PLANTS IN CLIMATAL ZONES BETWEEN 

 THE EQUATOR AND THE POLES. 



The description of the actual conditions of vegetation on the 

 surface of the globe is a subject embracing a vast amount of facts, 

 which are not only capable of being considered under many dif- 

 ferent points of view, but in many respects offer at present only 

 fragmentary materials for establishing principles. In the present 

 work, where only a limited space can be allotted to this depart- 

 ment, it is necessary to confine ourselves to a few of the principal 

 generalizations, calculated to give an insight into the characters of 

 the study, but confessedly very imperfect as representations of the 

 natural phenomena with which it deals. 



