Sidor som bilder
PDF
ePub

Keith's System of Physiological Botany. have the power of releasing their little prisoner. This is the singular structure of Aristolochia Clematitis, (Common Birtliwort,) a native of Britain.

The corolla of this flower, which is tubular, but terminating upwards in a ligulate limb, is inflated into a globular figure at the base. The tubular part is internally beset with stiff hairs pointing downwards. The globular part contains the pistil, which consists merely of a germen and stigma, together with the surrounding stamens. But the staniens being shorter than even the germen, cannot discharge the pollen so as to throw it upon the stigma, as the flower stands always upright till after impregnation. And hence without some additional and peculiar aid, the pollen must necessarily fall down to the bottom of the flower. Now the aid that nature has furnished in this case, is that of the agency of the Tipula pernicor. nis, a small insect, which entering the tube of the corolla in quest of honey, descends to the bottom, and rummages about till it becomes quite covered with pollen; but not being able to force its way out again, owing to the downward position of the hairs, which converge to a point like the wires of a mouse trap, and being somewhat impatient of its confinement, it brushes backwards and forwards, trying every corner, till after repeatedly traversing the stigma, it covers it with pollen sufficient for its impregnation; in consequence of which, the flower soon begins to droop, and the hairs to shrink to the side of the tube, effecting an easy passage for the escape of the insect.' Vol. II. pp. 353, 351,

None of the investigations of the physiological botanist appear to be more difficult and intricate, than those which are directed to the explanation of the excitability of the vegetable structure. In some cases, as we have seen, mere contact with the glaodular hairs, or irritable membrane of the plant, is a sufficient stimulus for the production of the most striking phenomena. These cases appear to approach most nearly to the nervous action upon the animal system, and would almost induce us to believe that vegetables are endued with sensation as well as vitality. In by far the greater number of instances of vegetable susceptibility, the immediate exciting cause is light, or temperature, or humidity: these stimulate the plant in proportion to their degrees of intensity. Here, the manner of action is either chemical, or mechanical, and is much more conformable to the changes produced in unorganized matter when operated upon by similar circumstances. Temperature and humidity doubtless produce their effects chiefly in á mechanical way, by the various degrees of tension or relaxation of the vegetable fibre. The presence or absence of light, combined with the above-mentioned causes, is productive of a great number of phenomena principally to be referred to chemical agency. During the darkness of the night, the numerous tribes of plants, as well as of animals, sink into repose. The great Linnæus has even ventured to trace the

[ocr errors][ocr errors]

alogy further, and to assert that vegetables sleep! Whatever.

the real nature of the changes which they undergo, certain it that, during the night, the functions of plants are, in some cies, materially different from those which they perform ring the day, and in others are totally suspended. While the 1 is above the horizon, carbonic acid gas is inhaled by the retable, and oxygen gas is evolved. When the light has deted, a precisely contrary elaboration of these two gases comnces; the carbonic being given out, and oxygene taken in. soon as the dews of the evening begin to fall, a universal nge takes place throughout the vegetable world. The flower gs its head, as if pensively awaiting the return of the holy shit' which no longer sheds its genial influence; the corolla es, as if unwilling to expand its delicate structure to te vinated by no sun-beam, and to be painted by no ray of ven.

ven the leaves appear to sympathize in the gloom ch prevails over the face of nature; those of many species ing theinselves back upon the stalk, or drooping till the rn of day! Such are the analogies between the vegetable

animal creation, which not only poets, but philosophers ght in tracing. To call this alteration or suspension of etable functions, their sleep, is doubtless to assume that they sentient, and is to give a plausible name to a phenomenon, rationale of which is but ill understood. If, however, the ogy be fancifal, it is innocent; it is scarcely possible that it ld mislead; and it conducts us to a more extended observaof an order of facts both important and interesting. nalogies between the condition of the merely organized and utellectual world, have beca traced not only in their func, but in accidental circumstances with which they are con

Our readers may, perhaps, smile when we tell them if men have clocks, so bave flowers : though many plants open their flowers in the morning and shut again in the evening, yet all Aowers do not open and shut at the

Plants of the same species, are, however, pretty regular hour, other circumstances being the same; and hence the daily ng and shutting of the flower has been denominated by botanists, dorologium Flore. Flowers requiring but a slight application of lus open early in the morning, while others requiring more, somewhat later. Some do not open till noon, and some, whose me delicacy cannot bear the action of light at all, open only at

such as the Cactus grundiflora, or night-blowing Cereus.' 445. e have vegetable weather-gages also, and of very delicate ture. That the changes in the state of the atmosphere are ated by corresponding effects in the habits of certain plants, act which suggests itself to the notice of the most trivial

obserter. Indeed, some of the most sensible of our philosophical instruments bave been constructed upon this very principle. The hygrometer is an instance in point. The most delicate of these instruments, is 'that which has been constructed by Major Kater, froin the beard of an Indian grass, the Andropogon contortum (twisted Andropogon), which, from its zero of perfect dryness, to the saturation by moisture, twists around its own axis ten or twelve times :* if, therefore, one end of the beard be fixed, and the other be attached to an index pointing to a circumference divided into one hundred equal parts, we have the enormous scale of 1000 or 1200 degrees. Haman skill, however, is not absolutely necessary to the existence of a vegetable weather-gage ; and yet we can scarcely subscribe implicitly to all the following assertions :

• The opening 'or shutting of some flowers, depends not so much on the action of the stimulus of light, as on the existing state of the atmosphere, and hence their opening or shutting betokens change. If the Siberian Sow-thistle (Sonchus Sibiricust] shuts at night, the ensuing day will be fine; and if it opens it will be cloudy and rainy. If the African Marigold, [Tagetes erecta] shuts after sevev o'clock in the morning; rain is near at hand. And if the Convolvulus arvensis [the Corn Bind-weed,] Calendula fluviatilis (C. pluvialis ? we presume the Small Cape Marygold,) or Anagallis arvensis [the Scarlet Pimpernell,] are even already open, they will shut upon the approach of rain, the last of which, from its peculiar susceptibility, has obtained the Dame of the Poor Man's Weather-glass. Vol. II. p. 446.

If we were inclined to pursue these accidental analogies, between the productions of art and the spontaneous results of unassisted nature, we might amuse our readers with a thousand popular examples. Dionæa muscipulu (Vepus's Fly-trap) has been before quoted; this curious plant is not only an example of irritability analogous to the nervous affections of animated beings, but the very machinery by which it entraps the uuwarg fly, bears a striking similarity to a rat-trap. The North American Saracenia purpurea (the Purple side saddle flower) has its leaves furnished with an anomalous appendage somewhat funnel. shaped, forming an artificial bucket adapted to contain water. Nepenthes distillatoria (the Ceylon Pitcher-plant) is still more sportively ingitative. From the end of the leaf issues a slender

* See an interesting memoir on the hygrometric properties of this curious, plant (the Oobeena Hoolou of the Mysore country) in the Asiatic Researches, Vol. IX. It was first brought to England in 1806 ;-Dut the mechanical construction of the instrument has been much improved by Mr. Jones, Optician, Charing Cross. Rev.

+ Throughout this article, wherever either the Scientific or the Trivial name has been omitted by our author,' we have inserted it Rev.

*

1

, Keith's System of Physiological Botany, 269 pedicle from which hangs a vegetable Pitcher, filled with limpid water; and the mouth of this natural amphora is furnished with a membranaceous lül or calyptra, opening on one side! Some writers bave fancifully imagined that a vegetable compass exists, in the structure of the concentric layers in tlie horizontal section of the trunks of trees. It has been urged that these do not striety eonform to the axis, the excess being attributed to the greater action of the sun on that part of the trunk which faces the meridian. This effect has been thought,

to be sufficiently striking and uniform to serve as a sort of compass, by which the bewildered traveller might safely steer his course, even in the recesses of ghe most extensive forest. But if this were the fact, it would certainly prove to be one of the most incommodious compasses, that ever was invented. For if the traveller must undergo the labour of cutting down a tree every time that he may want to know his bearings, it is to be believed that he will soon become tired of his instrument of observation.' Vol. I. p. 330.

Du Hamel has shewn that this fancied meridional law has no existence in fact, but that the eccentricity of the ligneous layers: 1 in the trunk, depends upon the position of the branches, and of the leading roots, the excess being always on that side in which the most nourishment is derived. Possibly a more decisive indication of the South may be derived from the aspect of a field of ripened corn." Bonnet has remarked that when the swollen grain bows down the stem, the inclination is not accidental, but is more or less directed to the South.

One more quotation shall close our allusions to the analogies. which subsists between the inventions of man, and the phenomena spontaneously exhibited by the vegetable tribe. It relates to the possibility of forming a Floral Calendar, by observing the precise season at which certain changes take place in individual species of plants. This idea was suggested by Linnæus; facts may be, in a philosophical point of view) a nation inust be..) in a very low state of refinement which has not better methods of regulating the operations dependant upon the progress of the seasons. He sensibly remarks,

* Although all plants produce their leaves, flower and fruit annually, yet they do not produce them at the same period or season...... But a great many circumstances will always concur to render the time of the unfolding of the leaves somewhat irregular.: ... Linnæus, who instituted soine observations on the subject about the year 1750, with a view chiefly to ascertain the time proper for the sowing of Barley in 1.1 Sweden, regarded the leafing of the Birch tree as being the best indication for that grain, and recommended the institution of similar para observations with respect to other sorts of grain, upon the ground of its great importance to the husbandman. But, however plausible , the rule thus suggested may be in appearance, and however, pleasing

[ocr errors]
[ocr errors]
[ocr errors]

it may be in contemplation, it is not likely that it will be ever mach attended to by the husbandman ; because nature has furnished him with indications that are still more obvious, in the evidence of his own feelings, as well as perhaps more correct ; as all trees of the same species do not come into leaf precisely at the same time, and as tbe weather may yet alter after the most promising indications..... The flowering of the plant, like the leafing, seems to depend upon the degree of temperature induced by the returning spring, as the flowers are also protruded pretty regularly at the same successive periods of the season.....

... Plants exhibit as much diversity in the warmth and length of time necessary to mature their fruit, as in their frondescence and flowering. . Such are the primary facts on which a Calendarium Flore should be founded. They have not hitherto been very mi. nutely attended to by botanists; and perhaps their importance is not quite so much as las generally been supposed; but they are at any rate sufficiently striking to have attracted the notice even of savages. Some tribes of American Indians act upon the very principle sug. gested by Linnæus, and plant their corn when the wild Plum blooms, or when the leaves of the Oak are about as large as a squirrel's ears.

The names of some of their months are also designated from the state of vegetation. One is called the budding month, and another the flowering month ; one the Strawberry month, and another the Mulberry month; and the autumn is designated by a term signifying the fall of the leaf. So that the Frer.ch revolutionists were anticipated, even by the Indians, in their new names for months and seasons.' II. pp. 449_453.

(To be concluded in our next Number.)

Art. VI. An Essay on the Chemical History and Medical Treatment

of Calculous Disorders. By Alexander Marcet, M, D. F.R.S. &c. &c. pp. 181. London. 1817. THE theory of calculary concretions constitutes a subject as

well of philosophical curiosity as professional interest; and as such, inay with propriety become a topic of our investigation. It is indeed right that inquiries of this nature should be made in some measure general, were it only that the circulation of knowledge among the profune and uninitiated, is calculated to keep the profession from indulging an indolent satisfaction with that kind and measure of science wbich has been acquired during the years of probationary studies. This feeling, althoughfar from being universal, is, we fear, by no means very uncommon; and it would probably be more prevalent and operative than it actually is, were it not that the ignorant practitioner runs the risk of having his lack of information detected by his better informed and more inquisitive patient. We would ever deprecate unprofessional interference with practical medicine, an art which can only be taught and acquired in the school of actual experience; but in the view we have just taken of the question, it is perhaps as well that the intelligent portion of the public should gain a little insight into the laws of living existence. Were it

« FöregåendeFortsätt »