CONTENTS OF THE INTRODUCTORY ESSAY. 
KL 
Preliminary Remarks. 
Sources of Information, published and unpublished, materials, collections, ete. . . 
Object of arranging them to discuss the Origin, Peculiarities, and Distribution of the Y aei of bagiau 
and to regard them in relation to the views of Darwin and others, on the Creation of Species A 
§ 2. 
On the General Phenomena of Variation in the Vegetable Kingdom. 
All plants more or less variable; rate, extent, and nature of variability ; differences of amount and bad 
in different natural groups of plants . i 
Parallelism of features of variability in different groups ; of individuals de AT species, genera, etc. 5, Si 
in wild and cultivated plants 
Variation a centrifugal force; the fendenty i in ^ed progeny of a Wie to deut further T their 
original types, not to revert to them . . " 
Effects of cross-impregnation and hybridization ultimately RR to permanence of dd onis 
Darwin's Theory of Natural Selection ;—its effects on variable organisms under varying conditions is to give 
a temporary stability to races, species, genera, etc. o. Wood da e . 
$ 3. 
On the General Phenomena of Distribution in Area. 
Cireumscription of Area of Species, and causes of it =: . « 
Relative Distribution of Natural Groups of Plants ; 
Insular Floras, and analogies between them and mountain ficia a bs the modi a ages of bar 
and other Floras . : : 
Existing conditions will sol — for existing e distribution . ; 
Effects of Humidity in modifying distribution :—effects of the Glacial Epoch, sid AN s views iden e 
$ 4. 
On the General Phenomena of the Distribution of Plants in Time. 
Outlines of the principal facts in Fossil Botany . ‘ 
Their bearing on the question of Progressive Seene ee dee Plants ; 
Progression and Retrogression of Vegetable Types . ER 
iii 
