ment of the flowers, and, in short, all that can be seen by the naked eye should be accurately expressed. It should also contain analyses of all the parts of fructification, magnified so much that every character may be distinctly seen; and this analysis, to be complete, should express the state of the organs of fructification, not only at the period of the expansion of the flowers, but in the bud state, and when arrived at perfect maturity. If to this the germination, and vernation, and highly magnified anatomical representations of the tissue and internal structure of the stem and leaves be added, the drawing may be considered complete.

But as the expense of preparing and publishing such drawings would be enormous, botanists usually content themselves with a representation of those parts only that are supposed to be most essential; such as the structure of the flower when expanded, and of the fruit and seed when ripe; and this is found, for systematic purposes, sufficiently complete, provided such details as are introduced are perfectly clear and

correct.

In order to enable the student, who is interested in this subject, to form a more distinct notion of the relative utility of botanical drawings, a reference to some of the most perfect that have yet been executed is subjoined.

As instances of the highest perfection of which botanical drawings are at present susceptible, the volume of illustrations of the structure of wheat, by Mr. Francis Bauer, preserved in the British Museum; the analysis of Rafflesia, published in the 12th volume of the Linnæan Transactions, and the microscopic drawings of the fructification of Orchideous plants, now in course of publication, both also by the same distinguished artist, may be justly said to be entitled to the highest place. Next to these come the drawings of New Holland plants in the Appendix to Captain Flinders's voyage to that country; and the three fascicles of figures of New Holland plants, by Mr. Ferdinand Bauer. A very high station is also claimed by Dr. Hooker's figures of British Jungermanniæ, in which great skill as an artist is combined with deep and accurate microscopic research. In all these works the details of analysis are carried to a great extent.

Among works in which fewer details are introduced, especial mention must be made of the drawings of Palms, and the figures that illustrate Dr. Von Martius's Nova Genera et Species Plantarum; Mr. Turpin's plates in Humboldt and Kunth's Nova Genera Plantarum, and Delessert's Icones Plantarum; and some excellent analyses of the parts of fructification of Rhamneæ and Bruniaceae, in his memoirs upon those orders, by M. Adolphe Brongniart.

Almost every scientific work of reputation of the present day contains figures which are formed upon the models of those now enumerated; from which they differ in the quantity of analysis that is introduced, a circumstance generally regulated by theprice at which they are published.

Of anatomical plates, the best are those of Kieser, in his Mémoire sur l'Organisation des Plantes; of M. Mirbel, in his Mémoire sur l'Ovule; of M. Francis Bauer, in his dissections of Orchideous plants; and of Mr. Adolphe Brongniart, in his various papers in the volumes of the Annales des Sciences.

I have mentioned these as instances of good drawings, because they are easily accessible, and incontestably are well adapted to improving the taste and execution of a student; but there are very many other modern works, in which the figures may be also studied with great advantage. Whatever bears the name of Francis or Ferdinand Bauer, Hooker, Greville, Mirbel, Poiteau fils, Redouté, Reichenbach, L. C. Richard, Sowerby, Sturm, or Turpin, may almost always be profitably studied.

BOOK VI.

GEOGRAPHY.

UNDER this head is to be considered the manner in which plants are affected by climate or station, and the conditions under which particular forms of vegetation are confined to certain zones of temperature; as the palms to the tropics, the true pines to extra-tropical regions.

This is one of the most curious and difficult subjects with which we can occupy ourselves. It embraces a consideration of the constitution of the atmosphere, and geological structure of all parts of the globe; and of the specific effects of particular conditions of climate and soil upon vegetation: all points upon which we can scarcely be said to know any thing. It involves the discussion of the plan upon which the world was originally clothed with verdure; and as Humboldt most truly observes, it is closely connected with "the physical condition of the world in general. Upon the predominance of certain families of plants in particular districts depend the character of the country, and the whole face of Nature. Abundance of grasses forming vast savannahs, or of palms or coniferæ, have produced most important effects upon the social state of the people, the nature of their manners, and the degree of developement of the arts of industry."

If we examine the surface of the globe, we shall find its vegetation varying according to its inequalities and its differences of soil; we shall see that the plants of the valleys are not those of the mountains, nor those of the marsh like the vegetables of the river or of dry grounds; it will also be seen that the vegetation of all valleys, all mountains, marshes, or rivers, has a similar character in the same latitudes. The

flora of the granitic mountains of Spain and Portugal is very different from that of the calcareous mountains of the same kingdoms; in Switzerland, Teucrium montanum always indicates a calcareous soil; and the same may be said of certain Orchises, ustulata, and hircina, for instance, in our own country. Hence it is inferred, that the differences in the character of vegetation, depend upon circumstances connected with the soil or atmosphere in which they grow. A great deal of ingenious discussion upon this matter will be found in M. De Candolle's article on botanical geography, published in the 18th volume of the Dictionnaire des Sciences Naturelles.

But as I do not find much that can be called positive deductions from such facts as have been ascertained, I shall, without entering into speculations as to the causes why one description of plants grows in one situation, and others in another, confine myself to an exposition of the positive facts which appear to have been hitherto distinctly ascertained.

It has been found convenient to divide the surface of the earth into different stations, when treating of botanical geography. In this part of the subject I shall adopt the arrangement and distinctions of M. De Candolle; agreeing with him that they at least indicate the most remarkable differences of station, if they are not susceptible of any rigorous definition. He admits the following classes:

1. Maritime, or saline plants; that is to say, those which, without being plunged in salt water, and floating on its surface, are nevertheless constrained to live in the vicinity of salt water, for the sake of absorbing what may be required for their nourishment. Among these, it is requisite to distinguish those which, like the Salicornia, grow in salt marshes, where they absorb saline principles, both by their leaves and roots, from those which, like Roccella fuciformis, exist upon rocks exposed to the sea air, and appear to absorb by their leaves alone; and, finally, a third class, such as Eryngium campestre, which do not require salt water, but which live on the sea-coast, as well as elsewhere, because their constitution is so robust, that they are not affected by the action of salt.

2. Marine plants, also called Thalassiophytes by M. Lamouroux, which live either plunged in salt water or floating on its surface. These plants are distributed over the bottom of the sea, or of salt water, in proportion to the degree of saltness of the water, the usual degree of its agitation, the continuity or intermittence of their immersion, the tenacity of the soil, and perhaps also the intensity of the light.

3. Aquatic plants, living plunged in fresh water, either entirely immerged, as Confervæ; or floating on its surface, as Stratiotes; or fixed in the soil by their roots, with the foliage in the water, as several kinds of Potamogeton; or rooted in the soil, and either floating on the surface, as Nymphæa; or rising above it, as Alisma plantago. This last division is very near the following class.

4. Plants of fresh water marshes, and of very wet places, among which it is chiefly necessary to distinguish those of bogs, of marshy meadows, and of the banks of running streams; and, finally, those of places inundated in winter, but more or less dried up during the summer.

5. Plants of meadows and pastures, in the study of which it is requisite to distinguish those that by their natural or artificial association form the turf of the meadow, and those others which grow mixed together with the greatest facility.

6. Plants of cultivated soil. This class has been entirely produced by the agency of man: the plants which grow in cultivated land are those which, in a wild state, preferred light substantial soils: many have been transported from one country to another with the seeds of other cultivated plants. Those individuals of the same species, which are found in fields, vineyards, and gardens, are often different in some respects, according to the peculiar manner in which they have been cultivated.

7. The plants of rocks; these pass by insensible gradations to those of walls, rocky and stony places, and even of gravel; and the latter soil, as its fragments diminish in size, conduct us by degrees to the following class. Rock plants offer some remarkable singularities depending upon the nature of the rock.