growing in favor here; and it is to be hoped that those makers who have heretofore made only one style of stand will soon offer both; so that buyers can choose their style of stand irrespective of their choice of makers. In objectives and accessories Tolles, Wales, Zentmeyer, Grunow, Spencer, Miller, and some other American makers were represented; also Ross, Beck, Powell and Leland, Crouch, Collins, Murray and Heath, Swift and Browning, of London; Nachèt and Hartnack, of Paris; and Gundlach of Berlin. Very low power cbjectives, 3 and 4-inch, were deservedly popular. The use of immersion objectives for all high powers seemed to be assumed by all members as a settled question. Few members, on the other hand, fall into the present fashion of high power objectives. — preferring to use lenses of 1-15 or 1-16, and downward, and gain greater amplification by other means than by reducing the nominal focus of the objective.

Dr. Josiah Curtis exhibited a micro-telescope, or microscope and telescope combined, made to his order by Tolles. It is an ordinary Cutter's clinical microscope, fitted with an extra tube carrying an object glass of one inch linear aperture and six inch focus, to which objective the compound microscope acts as an erecting eye-piece. Furnished with a proper support this makes an admirable pocket telescope, defining well at powers of forty or fifty diameters.

Mr. Tolles had mounted a 2 1-2-inch lens with the society screw on each side of the shoulder, so that it can either be screwed on in the usual position, or passed up into the body of the instrument and fastened there, giving, by approaching the eye-piece, about the power of a 4-inch lens at the usual distance. Microscopists have been accustomed to gain a lower power than could be focussed by their rack, by screwing a low objective into the drawtube and focussing upon the object through the empty nosepiece. The new plan of a reversible mounting is more convenient, and is applicable to instruments that have no draw-tube; unfortunately it cannot be used with the ordinary Binoculars. The lens, though of second class, was very good.

Mr. Tolles has also arranged a 4-inch objective in which a short working focus is obtained by a reducing lens in the rear. This reducing lens. for convenience, is mounted in a sliding tube, and gives when pushed in a fair 3-inch power. As a 4-inch the combination is extremely good.

Mr. Bicknell applies this expedient to ordinary objectives; placing in the draw-tube, instead of the concave amplifier sometimes used, an achromatic convex lens as a reducer, with which an extremely low power can be obtained with good definition, flat field, and working focus not inconveniently long. A 4 1-2 or 5-inch lens (solar focus) may be used. A low objective of two combinations may be divided, using one part as an objective, and placing the other in the draw-tube.

Dr. Ward had contrived a "clinical" compressor for use with the microscope of the same name. The clinical microscope is very convenient for examining mounted specimens, which is exactly what it is not wanted

for-except by teachers. He had used it for years in teaching, but not much as a "clinical." A glass slide to hold the object, with a thin cover held on by capillary attraction, is well for once, but does not satisfy a busy man. It applies to too limited a range of objects; and the cover is inconvenient to carry, awkward to handle, and easy to break. He had used Wenham's compressor until lately, but that is inconvenient under the springs of the "clinical" stage. The new compressor, figured below, is simple (and therefore inexpensive) and can be used with great facility both for clinical and class use, and for much of the ordinary work of the microscopist. It is reversible, except upon a large stage, in which case it would require a few pins to serve as legs. The want of parallelism is less than in most compressors, and is not inconvenient in clinical use. The two brass plates separate entirely for arranging the object or cleaning the glass. The upper plate fits into a notch filed in a ledge at the left of the lower, the centering of the two plates being secured by a pin through the lower and a notch in the upper. The screw which attaches them at the right is permanently fastened in the upper plate by a groove and a pin. It has a coarse thread, which may be cut double to screw out more rapidly, or the thread may be reversed near the centre so that it will at the same time raise the upper and depress the lower plate. Should a steadier motion be required, a spring may be riveted upon one plate to press against the other. The apparatus is adjusted for a glass of 1-20

Fig. 101.

Ward's Clinical Compressor,

inch below the object and 1-125 above, cemented upon the inner surface of the brass plates. This is strong enough to carry in the pocket safely; it can also be used with the parabolic illuminator, or with any objective or achromatic condenser except those of large angular aperture. Should thin glass be required for any purpose, a glass or tin cell of sufficient thickness to make up the difference should be cemented on one of the plates, or both if necessary, and the thin glass fastened upon the rim thus formed. Should no cell of suitable thickness be at hand, select a glass cover of the required thickness, fasten it with marine glue on one of the plates, punch out with a file the part corresponding to the opening in the plate, and then fasten the thin glass with Canada balsam upon this extemporized rim.

Mr. E. B. Benjamin, of New York, exhibited a microscope by Gundlach of Berlin. This was a small and cheap instrument, according to the English and American standard, but really admirable for its neatness of design and finish, and its general excellence of performance.

Beck's "popular" microscopes, binocular, were exhibited by Mr. C. E.

Hanaman and others. They have already vindicated their name in this country as well as at home.

Mr. Charles Stodder, of the Boston Optical Works, exhibited Cutter's clinical microscopes, and Tolles' students' microscopes, of various degrees of completeness and cost. These instruments are already too well known in this country to require comment. That they are thoroughly good of their kind is what is claimed for them, and is the least that can be said of them. In buying a students' microscope, however, the beginner should always be advised, in the writer's judgment, to have it furnished with a first class 1-inch objective or something very near it. So much of his early work is, or ought to be, done with this power, and his success as well as pleasure depends so much upon its light and definition, that it ought to be the last point economized upon. The sliding stage upon some of these instruments would seem to be easily convertible, for those who wish it, into a White's lever stage.

Mr. F. Miller, of New York, exhibited a good students' microscope of very low cost. It is chiefly notable for its large body, which admits a large eye-piece and gives a good field. Mr. Miller also exhibited excellent illuminating prisms and various accessories and objects, including Mōller's beautiful type plates.

Crouch's educational microscope had a larger body than even Miller's, admitting the use of the same eye-pieces as the first class stands. The advantage of this is enormous in the case of the lowest eye-piece.

Blankley's neat and convenient tank microscope, made by Swift of London, was exhibited by Dr. Ward. Also Murray and Heath's "seaside."

Of the general business of the subsection the most important was the appointment of a committee to report in relation to uniform standards in the power of objectives, eye-pieces, etc. President F. A. P. Barnard of New York, Mr. E. Bicknell of Cambridge, Mass., Dr. R. H. Ward of Troy, N. Y., Professor C. E. Pickering of Boston, Professor O. N. Rood of New York, and Dr. Josiah Curtis of Boston, constitute this committee.

ANSWERS TO CORRESPONDENTS.

J. J. H. G.-The Humming Bird you describe is the male of the common Ruby. throated Humming Bird (Trochilus rúbris L.). The female and the young are without the brilliant scarlet color on the throat seen in the males. After midsummer the scarlet throated individuals are far less numerous thon the others. There is but one species of Humming Bird in the Northern States.-J. A. A

J. M. J., Halifax. We will endeavor to name the collection of marine invertebrates for you.

S. A. W., Bucks Co., Pa. - Your fern is Osmunda regalis.—J. L. R.

S. L.. Freehold, N. J.-The caterpiller is that of Pieris rape Shrank, which was introduced from England to Quebec in 1856 or 1857, and is stated to destroy annually $240,000 worth of cabbages in the neighborhood of that city. It thence spread into New England, and is now common about New York and Philadelphia. It feeds concealed on the heart of the cabbage, while the two other species of Pieris, P. Protodice and P. oleracea, feed on the outer leaves.

The other specimens were the pupa of a species of Syrphus fly, which feeds on the plant lice, so abundant on the cabbage in the autumn. The Syrphus fly is of course very beneficial.

AMERICAN NATURALIST.

Vol. IV. — DECEMBER, 1870. —No. 10.

THE FLORA OF THE PRAIRIES.

BY J. A. ALLEN.

PROBABLY the vegetation of no two adjoining regions, both of which are situated between the same parallels of latitude and at nearly the same height above the sea, presents greater differences than exist between the vegetation of the fertile prairies of the Mississippi Valley and the forest region that extends from their eastern border to the Atlantic coast. To one who has always lived amid the diversified scenery of the Eastern or Middle States, where distant mountains almost everywhere bound the view, and forestcrowned hills and cultivated valleys so agreeably alternate as to dispel the possibility of monotony, a first view of the primitive prairies,

"The unshorn fields, boundless and beautiful,"

as Bryant has so felicitously described them, which

"stretch

In airy undulations far away

As if the ocean, in his gentlest swell,

Stood still, with all his rounded billows fixed

And motionless forever,"

is extremely novel and full of interest. But the prairies, "unshorn" of their primitive wildness will soon be things of the past, so great are the attractions they hold forth to the emigrant, and so rapid the transformation that follows their

Entered according to Act of Congress, in the year 1870, by the PEABODY ACADEMY OF SCIENC, in the Clerk's Office of the District Court of the District of Massachusetts.

AMER. NATURALIST, VOL. IV.

73

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settlement. Already there are few localities east of the Missouri where their primal simplicity and beauty have not already been more or less modified.

Great changes in the vegetation of a new country necessarily result from its settlement by an agricultural people, but the rapidity and ultimate completeness of the transformation greatly depend upon the relative susceptibility of the country to cultivation. Since vast areas of the prairies offer no obstructions to the revolutionizing plow, the astonishing rapidity of the change in the flora that follows its march can scarcely be conceived by those who have not witnessed its actual progress. No sooner is the sod inverted than scores of species of the original and most characteristic plants almost wholly disappear; in a few years the luxuriant wild grasses, overtopped with showy flowers, varying the hue of the landscape with the advancing season, have become supplanted by the cultivated grasses and the cereals, and that constant scourge of the agriculturist, the ever intrusive weeds. The timber no longer remains confined to narrow belts skirting the streams, for besides the newly-set orchards, rapidly growing kinds of trees, planted to afford shelter from the fierceness of the summer's sun and the fury of the bleak winter winds, everywhere diversify the landscape, while comfortable log cabins, or neatly painted, commodious houses give an air of civilization to districts that at no distant period were the undisturbed home of the buffalo and the elk.

Far more slow has been the change at the eastward, where the forests have slowly yielded to the axe of the woodman, and where much of the land is too uneven for cultivation. Here the forests, though in the longest settled districts perhaps once or twice removed, still cover no inconsiderable part of the country, and consist, for the most part, of the indigenous trees in nearly their original proportions, while the lesser shrubs and the herbaceous plants they primitively sheltered are still persistent, and to a great de