The continual extension of London is, however, rapidly encroaching upon all the old market-gardens, and they are obliged to move farther a-field: thus high cultivation, like a green fairy-ring, is gradually widening and enlarging its circle round the metropolis. The coarser kinds of vegetables are but sparingly grown in these valuable grounds, but come up in large quantities from all parts of the country; and some of the choice kinds are now reared far away in Devonshire and Cornwall, where they are favoured by the climate. It would be interesting to get an authentic statement of the acreage dedicated to fruit and vegetables for the London market, but we find the information unattainable. Mr. Cuthill calculates that there are 200 acres employed around the metropolis in the growth of strawberries, and 5 acres planted as mushroom-beds. Cucumbers were once very largely cultivated. He has seen as many as 14 acres under hand-glasses in a single domain, and has known 200,000 gherkins cut in a morning for the pickle-merchants. Strangely enough, they have refused to grow well around London ever since the outbreak of the potato disease. The disastrous epidemic of 1849, we have little doubt, had much to do with the diminished supply, for the cholera soon brought about the result desired by Mrs. Gamp, "when cowcumbers is three for twopence," prices quite explanatory of the indisposition of the land to produce them. The very high state of cultivation in the metropolitan market-gardens necessitates the employment of a large amount of labour; and it is supposed that no less than 35,000 persons are engaged in the service of filling the vegetable and dessert-dishes of the metropolis. This estimate leaves out those in the provinces and on the Continent, which would, we doubt not, nearly double the calculation, and show a troop of men and women as large as the entire British army. There are five marts in London devoted to the sale of fruit--Covent Garden, Spitalfields, the Borough, Farringdon, and Portman-markets,--besides a vast number of street offsets, such as Clare-market, in which hawkers generally stand with their barrows. Covent Garden is not only their type, but it does nearly as much business as all of them put together, and for that reason we shall dwell upon it to the exclusion of the others. At the first dawn of morning in the midst of squalid London, sweet country odours greet the early-riser, and cool orchards and green strawberry slopes seem ever present to the mind.