2 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



the more important of these are the Bacteria, which cause so many 

 of our worst diseases but in other instances benefit us greatly. 

 These and other ' border-Hne cases ', which include many of the 

 most primitive organisms living today, will be considered as within 

 our immediate sphere of interest. 



Fig. I illustrates some cases of plant-like animals ; several 

 animal-like plants will be described and illustrated in the next 



Fig. I. — Some plant-like animals. A, Hydra ( ■' 20); B, Obelia ( X about 12); 

 C, a Sponge (x about ^); D, a Coral (x ^). 



chapter. Defining and classifying such nebulous groups is one of 

 the trials and at the same time one of the fascinations of biology. 

 Geography is the study and description of the differentiation 

 and distribution of earthly phenomena, embracing all that composes 

 or affects the earth's surface — including its physical features, climates, 

 and products whether living or inert. A major branch is biological 

 geography, or biogeography, which for practical purposes is usually 

 subdivided along the main line of division of living things into two 

 kingdoms, so yielding plant geography and animal geography. Our 

 main subject, plant geography, also called phytogeography (from 



