across the Channel towards France just as county Dublin faces across the Irish Sea towards England; both are areas of early settlement and both lie in the main stream of traffic. In Kent we have to deal with a larger area (1,570 square miles), and a larger flora (1,160 species). We find that, of these 1,160 species, 146, or about one-eighth, are set down as owing their presence to man.[10] And so it is in all the more populous and highly tilled parts of our islands. This question of alien plants, their past history and present standing, is one of the most puzzling with which the student of our flora has to deal. In the first place, most of them have been in the country for a long time, and the record of their introduction is lost. Next, while many of them are confined to ground disturbed by man, and thus clearly exist under man’s protection--however unwillingly that protection may be afforded--others have mixed with the indigenous flora, won a place in the closed native vegetation, and might be ranked as true natives were it not that a study of their general distribution raises doubts as to the possibility of their having arrived in our islands unaided--doubts which their known occurrence in gardens tends to confirm. Take the case of the Yellow Monkey-flower (_Mimulus Langsdorfii_). This has quite established itself in our native flora, in some places ascending mountain streams far into the hills, in others mingling with the rank flora of muddy estuaries. It _looks_ as aboriginal as any of the plants among which it grows: but the facts that the genus to which it belongs is American (with a few species in Australia and New Zealand), that it itself is found native in the western States and not in the eastern, and that it has been long cultivated in gardens, furnish convincing proof that it is really an alien. But it is seldom that the evidence is so satisfactory as in this case. More usually the range of the doubtful members of the flora is continuous, extending from regions where they are truly native to others where they are undoubtedly exotic. For instance, many annual plants of the Mediterranean region have followed the spread of agriculture across the former forest areas of Central and Western Europe into our own islands. Plants native in France have been transported into England, and English natives into Ireland; east Irish plants have spread westward--sixty years ago, save for a single record of _P. hybridum_, _Papaver dubium_ was the only Poppy known west of the Shannon; now all four British species occur, several of them in many places. The flora of Europe, as pointed out already, diminishes in variety as we pass westward into the outlying areas. Those species whose aboriginal distribution stopped short of the western limit of the land had no doubt a fluctuating western or northern or southern boundary to their range, dependent on temporary conditions. Thus, a hard winter