196 A. G. Tansley. 
description of new species should be the first object of the botanical 
explorer. Even then something was done by the more intelligent 
collectors in the way of description of the vegetation as a whole, of 
the associations in which the species were found. But now, when 
the vast majority of species of flowering plants at least have been 
described, our attention must be more and more turned towards 
acquiring a knowledge of the associations or combinations in which 
plants occur. Even in the countries of Western Europe and America, 
the home of the races by whom the study of plants is mainly culti¬ 
vated, we are still very far from an approximately complete know¬ 
ledge of our plant-associations; though the work of Warming in 
Denmark, Flahault and his pupils in France, Graebner and others 
in Germany, many botanists in America, and quite recently several 
in Great Britain, especially in the north of England and in Scotland, 
has done and is doing something to take away this reproach. 
Schimper’s great work to which I have already alluded is a 
magnificent encyclopaedia of what was known at the date of its 
publication of the plant-associations throughout the world, know¬ 
ledge of which his own investigations on tropical floras contributed 
no small part. 
But we cannot, of course, stop at this first stage. The 
philosophers go on to tell us that the second and highest goal of 
scientific curiosity is to unravel the causes of phenomena, to go 
beyond the intuition of the gross appearances of what we see 
around us, to enquire as to their causation, or, to speak more 
precisely, to attempt the determination of the simple invariable time- 
sequences which exist in nature. 
When we consider the application of this principle to our 
ecology or topographical physiology, we see that it involves an 
attempt to determine why the plants which live together on a 
definite area with definite environmental conditions come to be thus 
associated—how they come to be and how they maintain themselves 
where they are, how they come to exhibit the morphological and 
physiological features they do exhibit, and what are their detailed 
functional relations to one another and to their inorganic sur¬ 
roundings. These indeed are topics on which our knowledge is of 
the most fragmentary description, about which we have still 
practically everything to learn. It is a much more difficult, as it is 
undoubtedly a much higher task, than the descriptive one. It 
involves careful and patient observation and experiment, and the 
application and adaptation of the methods of ordinary physiology 
to the solution of these special problems. 
It is obvious that the two stages of ecological study, the 
