Page:VCH Sussex 1.djvu/90

 A HISTORY OF SUSSEX My friend, the late Mr. H. C. Watson, in his Cybele Britannica, mapped out our island into plant provinces and enumerated the species which occur in each. What have been called types have been thus established. Certain species have been found to extend over all Britain. These are denominated as of the British type. Other species occur chiefly or exclusively in England. Some are limited to Scotland or the north of England and Wales. These are of the Scottish type with which we are not concerned. Plants which are found chiefly in the south-east of England and the counties adjacent to the German Ocean are classified as of the Germanic type. These include the chalk plants of which we have so many examples in Sussex including the insectiform Orchids. Another group of species is met with in the south-west of England and Wales, and occasionally extending far along the western and southern district. This forms what is called the Atlantic type, and is of peculiar interest to us in considering the distribution of the flora of this county. A few of them call for our special notice. One of these is the Cornish money wort (Sibthorpia Europæa), an exquisite little pink trailing flower, which, extending from the Scilly Islands into Cornwall and Devon, passes over west Sussex and occurs in east Sussex near Waldron, and no further in England eastward. This is a fact seemingly inexplicable. Scarcely less so is the case of the yellow bartsia (Bartsia viscosa), which beginning in Cornwall extends through Devon, Dorset and Hants, misses west Sussex, and reappears near Bexhill Common, where it has been established for more than fifty years. It is not found further eastward.

The question as to whether certain plants are or are not truly native is often asked, but is one on which botanists differ very widely. Mr. Watson divides our introduced plants into Denizens, Colonists, Aliens and Casuals. Denizens may be described as maintaining their habitats, as if native, but liable to the suspicion of having been originally introduced by human agency. Colonists as weeds of cultivated land, seldom found except in places where the ground has been adapted for their production and continuance by the operations of man. Aliens as certainly or very probably of foreign origin. Casuals as stragglers from cultivation. We have examples of all, which will be differentiated in our account of the Sussex botanical districts, and we need only observe that certain foreign species may be noted which are gradually taking up their abode with us, and have evidently come to stay, as for instance those farm pests, the clover dodder (Cuscuta trifolii), not long known here and very destructive; Bauxbaum's speedwell (Veronica Bauxbaumii), spreading rapidly in cornfields, and the lesser wart cress (Senebiera didyma), becoming common all along the Sussex coast, which manifests itself when trodden under foot by its pungent smell. To mention one other only, the sand mustard (Diplotaxis muralis), which is now becoming frequent, especially by the line of the London and South Coast Railway. This I first noticed but a few years ago, and observing it also near Torquay was able to add it to the flora of Devon.