Leaving the Museum, our little party repaired to the Conservatory, sometimes called the architectural Greenhouse; it is filled with a rich collection of Australian trees and shrubs, chiefly Myrtacess, Leguminosae, Proteaceae; the latter family so named in consequence of the very varied character of the stems, leaves, and inflorescence, yet agreeing in the essential character of the flowers and fruit. They are handsome evergreen shrubs, or small trees, of which the Banksias and Dryandras are the most remarkable. Their foliage, though harsh and rigid, has something of the Fern character; the flowers of the Banksias are arranged in bunches or tufts resembling a bottle-brush.

The next object was the Orangery, which is now mainly devoted to tender Pines, many of which are of great rarity and value; the noblest specimen in Europe of the Norfolk Island Pine, Araucaria excelsa, is placed here in winter. This tree is remarkable for its beautifully drooping and graceful branches, which almost vie with ostrich-plumes; small specimens are great favorites in our American conservatories, where every one who sees it regrets its want of hardiness. Araucaria Bidwilli has cones as large as a child's head; the seeds of it are eagerly sought after as an article of food by the aborigines of Australia. The collection here is necessarily miscellaneous; the plants are removed to the lawns in summer, and attract the eye of every one at all observant of trees. On quitting the Orangery, you encounter, alternating with the large beds, two lines of Deodars, designed for a long avenue of this stately and graceful tree; secondary lines are formed of Junipers, Cypresses, and other allied plants.

We must not, however, detain our readers with trees, or we should never get through with our "Day." We must proceed to the Great Palm House, or Stove, which is the glory of the gardens, constituting the largest iron and glass house in the world previous to the erection of the Crystal Palace. The extent of glass for covering this vast building is about 45,000 square feet; the ribs are inserted in enormous blocks of Cornish granite, placed in solid concrete. A substantial iron gallery runs round the whole at the height of thirty feet from the floor, ascended by flights of spiral staircases; this gives a fine view of the plants from above, and brings the spectator on a level with the summits of many of the loftiest palms. The whole of the iron of these stairs, etc, is covered with tropical vines in fell bloom; and this to us was one of the great beauties of the house.

But those "Princes of the vegetable kingdom," as Sir William calls them, the Palms, constitute the splendid and striking feature of the vast area; two of the loftiest kinds of cocoa-nut afford good examples of one group of palms with pinnated leaves, divided like the plumes of a feather. The two stoutest Palms are the West Indian or Jamaica Fan-palms, and are a good example of the second group, having palmate or fan-shaped leaves. So enormous are these specimens that each plant, with its earth and tab, are calculated to weigh 17 tons. Here, too, is the Date-Palm, producing the dates of commerce and of Scripture; also the plant producing the Palm-oil, now of so much importance. Sir William took particular pleasure in exhibiting to us from the gallery, the Plectoxoma elongata, presented by Dr. Willich, which, with its luxuriant foliage and very curious spring-stem, has the most singular mode of getting up in the world. The spines are digitate, or united together like the fingers of the hands, or still more resembling the wonderful conformation of the foot of the mole; its leaves are of vast length, and pinnated like the shafts of a feather, so long, indeed, that they, as well as the slender stem, need support Nature has come to the rescue; the main stalk of the leaf extends at the end into a lengthened slender tail, armed all along with strong defiexed hooks, by means of which, while running up among the stems of other trees and plants, and catching hold of their branches, the foliage and stem are propped in every position.

In the young plant, these spines are upright, and lie flat against the stalk of the leaf, not becoming reflexed till they are called forth by the wants of the pliant. Some bamboos have grown to the surprising height of 68 feet in 5 months; this includes a long period in their first stage, in which they make little or no progress, but after they have attained a certain altitude they rush up at the rate of 2, and often 8 feet a day.

There was first exhibited the tree of the Vegetable-Ivory-Palm, from the nuts of which so many ornamental things are now turned. It comes from Magdalena, New Grenada; it is named Phytelephas macrocarpa. The Wax-Palm, Ceroxylon andicola, was discovered by Humboldt in the Andes of New Grenada; the full-grown stem is covered with a waxy substance, having the same properties as beeswax. The visitor in London will observe that the streets are swept by a machine, with a brush of remarkable consistence. The tree which produces it is seen here, the Attalea fumifera; the coarse fibre of this and others separates from the base of the leaves.

The whole house is one vast magazine of tropical novelties, of which we can only mention one or two more. The Banana bears its curious fruit in abundance here, a single cluster often weighing 70 or 80 pounds. Perhaps the most remarkable object to the uninitiated will be found in the South African Elephant's Foot, Testndinaria elephantipes, so named from its resemblance, in the external surface of the gigantic root-stock, to the back of a tortoise, or to the foot of an elephant. Take it altogether, a visit to the Palm House at Kew will afford the visitor who has never been in the. tropics the greatest surprise and pleasure. We have a good example of some palms, as well as the Elephant's Foot, in Philadelphia, in the house built for the purpose by James Dundas, Esq., which will afford " an epitome view," and should not be neglected by amateurs who visit our city.

In the "Succulent House," we found a great display of the Crassula tribe, and Mesembryanthemums; many of the latter are remarkable for the resemblance in their foliage to the jaws of animals, whence they are Appropriately named felinum, tigrinnm, caninum, etc. The capsnles of others have the same hygrometric property as the entire plant of the famous Rose of Jericho, or the hygrometric Club-Moss, opening in wet weather into segments, resembling the petals of a flower, and closing in dry; a beautiful provision of nature, by which the seeds sow themselves at the only season suited, in those Cot sandy deserts, to their germination; after being gathered, they long retain this property, and may be made to open or shut, according as they are placed in a wet or dry atmosphere.

The Orchid house contains the specimens most in favor with cultivators at this time; the prices paid for them are sometimes almost fabulous. There is not a day in the year when some of them are not in blossom. Many are here seen attached to branches of wood, or placed in wire baskets, with moss and bark, or planted in the husks of cocoa-nuts, and suspended from the rafters, living, as it were, and flourishing on heat and moisture; the Vanilla, Vanilla aromatica, is one of these tropical Orchidese. Its long narrow pods afford the fragrant vanilla of commerce; it is from the hot parts of South America, being exported from Vera Cruz to the amount of 40,000 dollars annually. The King Plant of the Cingalese, Anoectochilus setaceus, as rare as it is beautiful, is here in perfection; we saw it, too, lately in the stove of B. A. Fahnestock, Esq., Philadelphia; the foliage closely resembles brown-greenish velvet, with the most exquisite network of gold. Other allied plants are green, reticulated, and spotted with white.

In the Tropical Aquarium is exhibited a group of different plants especially characterized by the varied coloring or marking of the foliage, often called " painted plants;" among them, the Caricature Plant, Graptophyllum hortense, many of the spots of whose leaves bear a very accurate resemblance to the human face, more or less divine - The fragrant lemon-grass will be remarked, and Sir William tells you it was a favorite tea with old Queen Charlotte; and he observes that the present queen takes an especial interest in these gardens. He lately sent her a basket of Osage oranges as a curiosity; "but," said the queen to him, with a pat of her fan, "how could you send such fruit for my table? Why, the lady-in-waiting cut one, and handed it to me; but really it was uneatable!" They do not ripen in England, and were an especial novelty there.

In the "Hardy Aquarium," among the greatest curiosities, is the celebrated Tussock-Grass of the Falkland Islands, Dactylus caespitosa; it is considered one of the most valuable coarse agricultural grasses, and, having braved the droughts and cold, and heat of England for several years, will be naturalized. It is slow in growth, and slower to form its great tussocks; they and the mass of foliage constitute thickets where wild cattle and more wild runaway sailors find shelter and protection, and both obtain food. Two sailors subsisted some time on the raw young shoots of this grass, which are, moreover, boiled like asparagus; vicinity to the sea, an equable climate, and cool atmosphere are deemed essential to its perfect success.

In the Aloe House, there is much to see and wonder at, especially the two lofty specimens of the Old Man's Head Cactus (or Cereus senilis), 14 feet high; it is called Senilis from the quantity of old wiry gray hair which crowns the summit. There is reason to believe, from its slowness of growth, and the reports of Mexicans, that these old fellows are hundreds, probably a thousand years old. No perceptible increase of size has taken place in the long period of their residence at Kew; there they stand, two sturdy pillars, and there they may stand for centuries..

Our English lady friend now exhibited marks of extreme fatigue. We made an effort, however, to reach the Victoria Regia House; but nature could no longer support her frame, and down on her knees she fell, a curious figure, with her parasol expanded. Sir William was truly polite, waited for her to rest; and we then proceeded, saw a lily bloom, and somewhere in a tropical fern-house we gazed at other things; pencil, however, could no longer do its duty, and we only remember the Great Stag's Horn Fern. It grows in Australia on the trunks of trees, but here, from the surface of a plank against the wall; the young stage of it is a small green leaf or frond, lying flat against the wood. It thickens with every succeeding growth of leaf; and this addition is alternately right and left over the older leaves, which die and contribute to the nourishment of the plant. A second plant was purchased for twenty-five guineas for Syon House.

Though our notes are not exhausted, we must here close our "Day at Kew" with a mere allusion to the great extent and value of the newly planted Arboretum, which promises to be the finest the world ever saw. We shall be paid for our labor if we have imbued one reader with an impression of the vastness, of the variety, and the value of the products of the vegetable kingdom, every possible specimen of which may be here examined.