154 LIFE : OUTLINES OF GENERAL BIOLOGY 



simplest form of "isolation", but the combination of circumstances 

 which secure fertilisation, diffusion, a second host, and so forth, 

 is often so subtle that it operates as an isolating evolution-factor. 



BIOSOCIAL COMPARISONS —It is an old story that the very 

 word parasite was taken over by zoologists from its classic usage, in 

 application to self-invited and pertinacious guests at the rich man's 

 table; and the inverse comparison has again become increasingly 

 frequent in modern times, thus frankly inspiring the well-known 

 Parasitism, Or^aftic ami Social, by Massart and Vandervelde, 

 the latter since eminent as a political leader in Belgium, and to 

 this day helpful at Geneva. And many years ago, long before that 

 book, it was no small surprise to one of us when writing the article 

 "Parasitism (Animal)" in the Encyclo pcedia Britannica (9th edition), 

 and when also comparatively fresh from a sound training in classical 

 p<jlitical economy, to note the amazingly close similarity, often 

 wellnigh to identity, between these two distinct and separately 

 developed presentments of fully attained material success in life. 



ILLUSTRATIONS OF PLANT ECOLOGY 



The Ecology of Plants, as we have already explained, is the study 

 of their relations to their environment, and to one another, and to 

 animals. It is a physiological inquiry, but it deals with plants in the 

 plural, in their associations and linkages, not with the life of the 

 individual plant. It is in the main the old-fashioned "Natural 

 History of Plants"; and it is far more of a "field science" than plant 

 morphology or individual physiology. The ascent of .sap is a problem 

 in the physiology of the individual, though it has its ecological 

 aspect, in reference to the seasons, and to particular surroundings; 

 but the inter-relations between flowers and their insect visitors are 

 typical problems in ecology. 



HISTORICAL NOTE— The word ecology is due to Haeckel, who 

 used it to denote the study of organisms in their relations with their 

 animate and non-animate environment. As a synonym the term 

 "Bionomics' ' was suggested by Kay Lankester ; but Ecology is prefer- 

 able in its suggestion of studying the living creature in its home 

 or oikos. Very unfortunately the general term "Biologic" is used in 

 exactly the same sen.se by many German naturalists. While the 

 study of plants in relation to their habitats, enemies, pollinators, 

 .seed-scatterers, para.*;ites, and so on, has a long history behind it, it 

 is only within the last fifty years that plant ecology has been taken 

 very seriously. The study of the linkages between flowering plants 

 and their insect visitors received a great impetus from Darwin, who 



