IN earlier days botanists were principally occupied with the compilation of a record of species and the building of that record into a system which might exhibit the relationship of species to species, genus to genus and so on. Without that work it would be impossible to consider what the effect of species upon species in a natural population may be. Nevertheless, there is in principle nothing more difficult about discovering the composition of a population of species than there is in taking a census of the population of the British Isles. The latter job is a big one because of the number of persons involved, and the diversity of occupations makes classification troublesome at times, but it is, after all, only a matter of finding out who is in a particular place and what he does when there. The questions of how he came there and how he continues are comparatively simple extensions of the inquiry. The fundamentals do not demand any more elaborate
apparatus than a pencil and notebook. We can investigate a population of species in nature by equally simple methods.
Unfortunately there is the difficulty mentioned earlier : you can ask a man his name, age and occupation; a plant is unable to tell you and so you must know how to find them out for yourself. For the British Isles we know the composition of the plant population by species tolerably well : in other words, the discovery of a very distinct species of flowering plant hitherto unknown to botanists would be a noteworthy event. The catalogues of British plants are, at any rate, as complete as for any country, and the identification of the majority of species is not really very difficult. Given a piece of ground occupied by plants, it is within the capabilities of any person who is interested enough to take the trouble, to find out what species are there and what kind of job they are doing. This is work well worth doing, especially if carried on for the same territory all the year round and supplemented by abundant photographs. The extensions of the inquiry— how the species came to be where they are and what conditions make it possible for them to stay there, or force them to give way to other species—are not so easy and are better left alone for the moment.