INTRODUCTION ix 



peculiarly situated a group of islaiuls as the British Isles, the flora must be very 

 varied. The world trade ot the British Isles brings to us many aliens, and the 

 migration of birds, the lines of which lie across these areas, is responsible for the 

 occurrence of many plants here that grow in far-distant regions; and, similarly, 

 the Gulf Stream and prevalent winds may be the deciding factors in other cases. 



.As to the general character of the flora and the status of many species, and the 

 occurrence of endemic species, Mr. Druce in his report of the floristic results of 

 the International Phytogeographical Excursion, 1912, writes: "Whereas many 

 leading British systematists have been extremely reluctant to ackiiowedge that 

 the British Isles contained endemic species . . . yet, as one would expect, a 

 more minute and critical study of plant forms . . . has led to well-marked 

 differences being established between many of our island species and their homo- 

 logues on the mainland of Europe". Referring to some remarks by Dr. Graebner, 

 on the difference between British and Continental forms of Sedutn acre (the British 

 type is distinguished as Sedutn Dnicei), Mr. Druce adds: "This statement is 

 borne out by one's own experience; one sees that the common species of Jersey 

 have a different facies from those of our Midlands, while those of the north Scottish 

 coast possess a distinct individuality from those of Devon and Kent. But it is only 

 exceptionally that specific distinctions can be found. This range of variation, 

 differing necessarily in degree, however, suggests that we may be unwise when 

 working with critical forms to attempt to identify the microspecies of Geraiimm, 

 Erodium, the Melanitnn Violas, and the critical species of Rosce, Ettphrasite, 

 Hicracia, and Taraxaci, with Continental names. In many cases I strongly 

 suspect that the British plants are sufficiently distinct to warrant them being 

 described and named. Indeed, as will be seen, two of our British plants, Erigeron 

 alpinus and Mclampyrum pratense, should bear. Dr. Ostenfeld suggests, other 

 names. And, if evolution be a fact, we might be prepared to expect that these 

 plants, living for so long under different climatal conditions and geographical 

 position, should have evolved a facies of their own." 



The influence of man over the character of the present flora has been emphasized 

 in previous volumes. His relation to the status of plants, as defined b_v Watson, 

 has been ably defined by the Rev. E. A. Woodruffe-Peacock in Natural Habitats 

 and Xaiiveness, where he writes: " In relation to man as a predominating factor in 

 the botanical problem, all we have to set ourselves to disentangle is, ' what is 

 permanent, and what is transitory?' The former is natural, the latter accidental, 

 semi-alien, or alien. No other criterion appears to be possible. It has the advan- 

 tage of being simple and practical. It may be diflficult to say whether a given species 

 is 'native, denizen, colonist, or casual' under a certain environment, but it is 

 easy enough to ascertain whether it is permanent or transitory. It is not difficult 

 to demonstrate whether a plant is found in the majority of fitting situations, or 

 whether it is peculiar to one locality, or at most a few, under suspicious circum- 

 stances, under the same conditions of growth. 



"To help in this respect, and to escape from the difficulties and perplexities 

 of the Watsonian system of terminology, I propose to class all species into various 

 categories, as they stand in an intimate or more distant relation to man and his 

 undertakings. Their position in a category or categories will at once settle their 

 status. Samples only can be given here: P'ollowers (i) of man, (2) of cultivation, 

 (3) of commerce. Frequenters (i) of broken ground, (2) of waste ground, (3) of 

 pasture, (4) of meadow, (5) of woodland, (6) of roadside hedges, (7) of field hedges, 

 (8) of lakes, (9) of ditches, &c., are much more simply applied, even though the 

 phrase lacks the sweet simplicity of the Watsonian word. Both should contain a 



