the chalk hills on the west of the town, and to ascend Creechborough. These chalk hills are of a much harder substance than those of Kent and Sussex, steep on all sides, and thence with a more mountain-like appearance, and the strata are highly inclined. In Botany they afforded me nothing but Brachypodium pinnatum, which is exceedingly abundant on the whole range. Creechborough is a somewhat conical point of sand and gravel, belonging probably to the plastic clay, and apparently overtopping the adjacent chalk hills, but the day was so thick I could nowhere see the horizon, and the rain came on heavily while I was on Kingsbury, and continued till I got back to Corfe Castle, preventing my farther examination of the sand and clay pits for the Trifolium resupinatum.

Saturday was fine, and as the glass was rising, I set off for Studland. The road keeps near the chalk hills and above the barren heaths, although it is itself, I believe, almost everywhere on the plastic clay beds. It is remarkable that these beds, where they climb up the back of the chalk hills, as on this road at Kingwood Heath and at Creechborough, have not the extreme barrenness of the lower beds. The strata are, I believe, nearly horizontal, and not inclined with the chalk, at least such is the notion suggested by the appearance of the clay-pits: these upper parts may therefore perhaps belong to a later formation. Over all this tract of country we find a Rubus much like R. plicatus, but the stem more arched and much more prickly. Mr. Borrer suggests that it may be R. nitidus; for my part, I hardly venture to form an opinion on a Rubus, but in this plant the shoots are decidedly arched and hairy, the prickles curved, and the stalk of the panicle not polished. The panicle, too, seems to be nearly simple,

in all which it differs from Babington's idea of the Rubus nitidus. On this walk, as in that of Thursday, I found Orchis conopsea abundant in dry meadows, without smell. The descent into Studland was cheered by Trifolium glomeratum and subterraneum, and Medicago denticulata and Lotus hispidus, a pretty group of one tribe growing together. On the beach at Studland, Cynodon dactylon was very strong and vigorous, but not yet showing any of its "horns," and beyond it, in considerable abundance, but for the most part not yet in flower, Filago Jussiei of Cosson and Germain. This is undoubtedly the Gnaphalium pyramidatum of some authors, enumerated as a species or as a variety of F. germanica, and I see no reason to doubt its being the Filago pyramidata of Linnæus, though Cosson rejects this idea and Koch reasons against it. Linnæus does not describe the heads, but the flower (i. e. the compound flower) as pyramidal,

which is strikingly the case in the present plant. The observations of Messrs. Cosson and Germain are abundantly sufficient to stamp it as a good species. Passing over Ballard Down, I observed several of the corn plants of a chalky soil, as Linaria Elatine and spuria, and all these occur, not only on the chalk and limestone, but also on the intervening clay and loam of the Wealden formation.

After church on Sunday I walked along the shore to the foot of Ballard Down, and then turned inland along the foot of the down. In one of the little drains that trickle from the cliff I got Scirpus Savii, and at the foot of the downs Rubia peregrina.

On the Monday morning I walked up Nine-barrow Down, one of the highest of these chalk hills. Just before reaching the open country I fell in with two tufts of Iris fœtidissima, with yellow flowers. 1 was the more struck with this, as Mr. Borrer had just been mentioning that he thought he had seen such a thing in the gardens at Hampton Court.

My chief object at Swanage was the Phalaris paradoxa, but the discoverer, Mr. Hussey, was not at Swanage. However, I found that Mr. Willcox, a surgeon of the place, was well acquainted with the plant and its habitat, and he kindly undertook to conduct me to the spot, premising, however, that the field had become a potato-ground, and that none of the plant was to be found. We of course looked in vain. It seems to have been pretty abundant in a space of about thirty or forty yards square, in one corner of a corn-field, and there was no account of any foreign seed having been sown there at any time. The soil seemed rather a stiff loam on the Wealden beds, some of which on the Isle of Purbeck are very sandy, but that is not the case in this field. Leaving this field and crossing a lane we came on the yellow variety of Iris fœtidissima, which may therefore be presumed to be not very uncommon in this neighbourhood. A Daucus abounds here, which I take to be the maritimus of Withering and hispidus of De C., at least as far as regards the French plant, but of course the fruit was not yet formed. Mr. Willcox informs me that the poor employ it as a diuretic. Mr. Willcox possesses a very interesting collection of the fossils of the neighbourhood, particularly of the fishes found in the Purbeck beds, and also some leaves from

the plastic clay.

On Tuesday I proceeded by stage to Wareham, and thence by railroad to Wool. There I engaged a lad to take my luggage to West Lulworth, and proceeded myself on foot, but the walk is not interesting; yet had the day been fine I should probably have found amuse

ment in the distant views; for the road lies very high for a considerable portion of the way. The interest of West Lulworth lies entirely in its singular broken shore, where we see the Purbeck limestone rising from under the chalk hills, with more or less of the strata of the Wealden and of the green sand between them. In one or two places the strata are absolutely reversed, and the green sand appears to rest on a chalk very full of flints. The chalk strata are very much inclined, or quite vertical, as in the Isle of Purbeck, but the singularity is, that there and here, these highly inclined strata are backed by horizontal strata of chalk. A little way west of West Lulworth is a perforation in the limestone rock called Duddle Door, and near this we find abundance of Statice spathulata. The leaf is rather broad, with an uninterrupted margin continued behind the mucro. In Sussex we have a variety with a broader leaf, but in which the mucro is usually or always terminal. Crithmum maritimum is abundant both on the chalk and the limestone, and on the chalk a form of Arenaria marina, with a very stout, woody root, showing several concentric circles. Most botanists describe A. marina as an annual, I doubt if correctly, and Babington inserts a p. ?. Erythræa latifolia, I believe, occurs on the intermediate Wealden, but I am not very confident in my power of determining this species. In the little bay between Duddle Door and Lulworth I observed a good deal of a Brassica which I had noticed in August, 1837, in this neighbourhood, distinguished from B. oleracea by the turgid and seed-bearing beak. My friends Mr. Borrer and the late Mr. Janson have assured me that it retains this character in its progeny, and both agree that the plant is distinguishable in all stages, though it would perhaps be difficult to describe the difference so as to identify the plant independently of the pod. I found this plant again the next day, on the little opening to the shore which exists at East Lulworth, on the chalk cliffs. did not anywhere observe it on the limestone, but Mr. Willcox informed me that the quarry-men in Purbeck make use in the spring of a cabbage they find on the cliffs. Query if this is the same, and also if the plant of Dover cliffs have a seed in the beak. De Candolle has a section of the genus Brassica distinguished by having a seed in the beak, but these, with the exception of B. Richeri, belong to the genus Erucastrum. The German and Italian Floras do not mention B. oleracea as a wild plant, and they have no species to which this can be attributed; for though two or three of them have constantly or occasionally seeds in the beak, the descriptions are very different in other

I

respects.

Loiseleur mentions B. oleracea as native of the Atlantic shores of France, which Duby limits to those of Normandy.

On the top of the chalk cliffs near Duddle Door grows Erodium maritimum, and on the banks above a large corn-field, east of West Lulworth, there was abundance of Ophrys apifera and a few plants of Orchis ustulata. These are all the rarities I noticed in the neighbourhood. On my return through Wareham I examined a plant which is probably the Enanthe fluviatilis of Coleman, though the description does not quite agree. The place where I was able to get at it was just above a mill on the Piddle, a little above Wareham, in a gentle current, and the water perhaps two feet and a half deep. The stems there were erect, very hollow, not angular, and somewhat thickening downwards to the root, but with a slight contraction between the root and the stem, with numerous whorled fibres, but not so numerous or so thick as in E. Phellandrium. In other places, in a stronger current, the stems were drawn out as described by Coleman, and appeared not to thicken from the middle downwards. The submersed leaves exactly correspond with his figure and description; but though I feel confident that they belonged to the same plant, I could not get up any in connexion with the flowering stem, which produced no leaves entirely under water. It does not appear that C. Phellandrium has any of these submersed leaves at this time of year. The plant is abundant in the Frome and Piddle, and also in the Avon, and probably in the Stour, flowering freely, but at present the seeds are of course very imperfectly formed. Wareham stands on a sandy point of land between the rivers Frome and Piddle, and its ancient boundaries are marked on three sides by an earthen bank, forming a pleasant walk. The fourth is formed by the river Frome. This projecting point, though sandy, is of not so barren a soil as the heaths which occur at a little distance both on the north and south sides of the town. From Wareham I returned by railway direct to

Lewes.

JOSEPH Woods.

Lewes, August 1, 1848.

On the Number of Botanical Species to a Square Mile of Ground. By HEWETT C. WATSON, Esq.

IN the 'Phytologist' for this present month Mr. Coleman intimates his opinion, founded upon observations in the county of Hertford, "that if a square mile be taken at a venture, its flora may be considered a good one if it amount to as many as 200 species" (Phytol. iii. 220). Were it possible for a botanist to map out the whole of Britain into square mile sections, and fully ascertain the species of each section, I think it probable enough that 200 species to a mile of rural surface might prove over rather than under the average number. In a general sense, I may therefore concur with the opinion expressed by Mr. Coleman, although there is some degree of discrepancy between us.

On some of the elevated moors of Scotland, where the surface is pretty uniform, and is still left almost in a state of nature, many square mile sections might likely be found each containing less than one hundred, possibly even less than fifty species of flowering plants. But in England I doubt not that many square mile sections might also be taken, within which a botanist would find more than 300 species, and in several of them more than 400.

By way of putting this to a practical test, since reading the valuable paper by Mr. Coleman, I have reckoned up the species on a square mile of surface immediately around my own house. I find that nearly 400 species can be enumerated as certainly wild within the extent of the mile; and if adding to the list about a score of introduced and unsettled species, the number may be raised to 410 species or upwards. By enlarging the boundaries so as to extend the single mile into a space of twenty-five square miles, I find that my enumeration will give 660 species, including aliens and unsettled species or varieties. The whole county of Surrey would probably be found to include upwards of 800 species, fully double the number in the single square

mile.

I take the square mile immediately around my own abode, as being that one with the productions of which I feel myself most familiar. It presents considerable diversity of situation for plants, with little variety of soil; the latter being either clayey loam or gravel, with a few very small patches of sand. The mention of a dozen generic names will indicate tolerably well the variety of situation; namely, Hydrocharis, Actinocarpus, Calluna, Jasione, Verbena, Lycopsis, Helminthia, Briza, Silaus, Hyacinthus, Circæa, and Orobus.