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ces formed by their combination, he proceeds with the different veffels of plants, viz. air, and lymphatic veffels, the cellular texture, the fap, and their tranfpiring pores. Where he treats of these, we find, in page 243, a blunder which muft have efcaped either the author or tranflator: cubic has been used inftead of fquare. He fays, Hedwig counted in the Lilium bulbiferum, in one furface of a fingle leaf, 577 apertures in one cubic line. A cubic foot would therefore, according to this obfervation, have about 998,145 apertures.' The calculation too, if it has been made according to the table given in page 10, is incorrect. After difcuffing the temperature and phenomena of the germination of plants, he proceeds to the ftructure of their different parts. In mentioning the ftructure of the bud, p. 273, he fays, Each bud unfolds a branch. with leaves, which, at the bafe of each petiole, again produce buds. In this manner their growth continues. But this evolution of buds from buds, would continue without ftopping, were it not fo regulated that each bud, as foon as the bloffoms and fruits are perfectly formed, decays. We confefs we do not understand what he means by this, unless he means to affert what has no foundation in nature. He advances fomething to the fame purpose, when treating of the structure of vegetables, near the cominencement of his phyfiology; against which we have already entered our proteft. We fhall now give our reafons. Every branch that proceeds from a bud, produces one or more buds at the axilla of each of its leaves, which may be either flower buds or branch buds, according to the age and vigour, or nature of the tree; for there are fome trees which produce tir flowers in buds diftinct from thofe which produce. branches, and others that do not. The peach, the cherry, the lilac, and my other trees and fhrubs, may be given as examples of the former: in thefe, the flower buds, after fructification has been completed, die, but do not occafion the death of the branch on which they ftand; and, fo anxious has Nature been for the production of branches, that it very often happens, in trees of this kind, that a branch bud is found in the axilla of the fame leaf, with one or two flower buds. Of the latter, many examples may be given; fome of which produce their flowers from the fides of their branches, ex. gr. the Vine and Paffion flower: in thefe, the peduncie only dies after the decay of the flower, or ripening of the fruit; but the branch from which they proceed, continues to grow. Or ers produce their flowers at the extremity of the young branch, ex. g. the Rofe: in thefe, the flower, with its peduncle and part of the extremity of the branch, only decay; but the under part of the branch, where completely formed leaves have ftood, continues to live, and is capable of producing branches.
The formation of the leaves, the inhalation and exhalation of plants, the circulation of their fap, the fleep of vegetables, their green colour and inclination towards the light, the duration and decay of the leaves, and the evolution of the flower, fucceffively occupy his attention. On most of these subjects we find much reafoning, and not a little hypothesis; but not so many facts adduced in fupport of fome of his affertions, as we think neceffary to produce conviction.
When fpeaking of the food of plants, (p. 281.) he says,
The chief food of plants confits of carbon and hydrogen; the hollow air veffels carry the oxygen gas, which was formed during the day, out of the plant; and in the night time, when the rays of the fun are wanting to evolve more oxygen gas, they exhale, through the pores of the cutis, carbonic acid gas, which they received from the ground, and which, for want of light, they could not keep fixed. '
This is not enough for one unacquainted with the fubject; and one who knows fomething of it, knows, that there is a difference of opinion concerning the food of plants, and therefore would expect fomething more than bare affertion. Befides, the subject merits more attention; for, the knowledge of what conftitutes the food of plants, may be useful to the practical agriculturist, as well as the ftudent of botany,
He treats very fully of the impregnation and generation of plants, a fubject which merits more attention than is generally paid to it. Many are difpofed to doubt the fexes of plants alto gether; and few of those who are convinced of its existence, have thought of turning their knowledge of it to account. We are perfuaded, many good varieties, both of ornamental and useful vegetables, might be obtained, by impregnating one plant with the farina of another nearly allied to it. Thus, a native vegetable might be impregnated with the farina of a species, the inhabitant of a warmer climate, poffeffed of fuperior qualities, and a hybrid be produced, poffefling fome of the properties of its exotic parent, and yet hardy enough to endure a feverer climate. Vegetables producing fruit or roots of fuperior fize, but defective in point of flavour, fweetness, or nutritive properties, might be improved by commixture with other varieties or fpecies poffeffed of these qualities, but deficient in point of size.
Empedocles and Anaxagoras attributed fexes to vegetables, and Theophraftus takes notice of the difference of fex in the Coryza and fome other plants, and fays that the fruit of the Palm will not germinate unless the flowers of the male be shaked over the fpadix of the female. But the notion which the ancients had of the difference of fex in plants, was by no means accurate. Pliny, in particular, fometimes mistakes the male for the female, and calls
plants male and female, which are hermaphrodite. Sir Thomas Millington was the first who fixed on the ftamina as the male. organ, and piftillum as the female. From that time the existence or nonexistence of fexes in vegetables, has been a matter of controverly among botanists. To enumerate all the arguments that have been employed by the advocates on both fides, and the ex-. periments on which they were founded, would both be tedious and unneceffary; fince the production of vegetable hybrids, by impregnating one fpecies with the farina of another (an experiment which has frequently been repeated), has not only proved the existence of fex in vegetables beyond controverfy, but has fhown the particular kind of generation which takes place in them.
M. Willdenow, after taking notice of the principal theories of generation that have been propofed, proceeds to give his opinions of each of them. We fhall pass what he fays of Equivocal generation, because it has been long exploded.
Of the Animalcular fyftem, he fays (p. 325.),
The theory of Animalcula in the femen of animals being carried over to the ovarium of the mother, where the new animal is formed, has Leuwenhoeck for its author. Some, therefore, in the vegetable kingdom, affumed preexifting germs or corcles in the pollen, which, in the mother's ovaries, unfolded themselves, into the future plant. A very zealous supporter of this opinion, was Mr Gleichen. Some even went fo far as to fee, under the microscope, small affes in the femen of an afs, and fmall lime trees in the pollen of a lime. Strange things may be feen, if perfons are difpofed to fee them. Koelreuter's obfervations, of which immediately, at once overthrow this doctrine.
The fyftem of preformation, which in former times was much in vogue, is not, even by its most zealous admirers, much infifted on in, the vegetable kingdom. Spallanzani, who, in animals, by means of tedious experiments, attempted to prove the preexiftence of the animal before the impregnation of the ovum in the ovaries, fincerely confeffes, that there is no preexistence of vegetables like that in animals.
The Epigenefis, or generation by a commixtion of the fluids given out both by the male and female, is what moft phyfiologists now affume as the only true theory of generation, both in the animal and vegetable kingdom. Koelreuter confirmed it by numerous experiments, of which we shall mention only one. He took of the genus Nicotiana, the Nicotiana ruftica and paniculata. The firft he deprived of all its ftamens, and fecundated its piftil with pollen of the last species. Nicotiana ruftica has egg-flaped leaves, and a fhort greenish yellow corol; Nicotiana paniculata, a ftem half as long again as the former, and roundish, cordate leaves, and much longer yellowish green corols. The baftard offfpring of both, kept in all its parts the middle betwixt the two fpecies. He tried the fame with more plants, and the refult accorded perfectly with the firft.
VOL. II. NO. 21.
• Were we therefore to admit the animalcula feminalia, the hybrids could not neceffarily have differed in form from the male plant; and, on the other band, were the evolution fyftem founded in nature, they would have the fame form as the female plant. The hybrid, however, was a medium between both; it certainly, therefore, adopted some parts both from the father and mother, and was formed by Epigenefis.
Koelreuter, however, could only obtain hybrids by intermixing fimilar plants. Diflimilar plants never produced them, even though, according to our fyftems, they belonged to one genus. It appears that nature thus avoids unnatural mixtures.
The inftance of mules not generating, as it was once believed at leaft, induced many philofophers to make it an axiom, that hybrids are barren. But we now know a good many inftances in zoology, of hybrids being very productive; and even the inftance of mules does not prove any thing, as in warm climates they are fometimes prolific. Koelreuter likewise found hybrids of various fpecies of tobacco, and fome more plants, to be fterile; the pittil in them being very perfect, but the flamens not completely formed. But there are now feveral inftances of hybrid plants which retain their original form, and propagate themelves. I fhall only mention a few, with their parents.
Sorbus Hybrida; the mother was Sorbus aucuparia, and the father Cratagus aria.
Pyrus hybrida; the mother was Pyrus arbutifolia, and the father Serbus aucuparia.
• Rhamnus hybridus; the mother was Rhamnus alpinus, and the father Rhamnus alaternus.
What mixtures do not the species of Pelargonium produce in our gardens? All plants of the 21st, 228, and 23d claffes of Linræus molly generate prolific hybrids. Linnæus wrote a particular treatise on hybrids, in which he attempted to explain the origin of fome particular plants; but unfortunately he has given nothing but hypothefes, his chiervations not according with experience. Should it not, from the observations made with regard to the hybrids of the animal and vegetable world, be laid down as a rule, admitting fome exceptions, that all hybrids are productive, but that fome only want a warm climate to unfold the male femer? I do not attempt to eftablish this rule as quite certain; I should be happy, on the contrary, would philofophers con£ider this fobject more accurately, and attend more to the hybrids of different clientes, on perpofe to fettle the point.
• Bu Koelreuter made fome experiments, which put the doctrine of Epigrmy's bevond all doubt I thail only mention one of his obfervats as an inftance. He ebraired, as we have feen, a hybrid from the Notias ruftica and pariculata. Nie tiana ruftica was the female plart, and paniculata the mic. The hybne, nike all the others which he brot ght up, had in perfect damers, an kept the miscle between the two free is He afterwards impregnated this hybrid with Nicotiana paniculata, and got plants which much more reliabled the l24. This
he continued through feveral generations; till, in this way, by due perfeverance, he actually changed the Nicotiana ruftica into the Nicotiana paniculata. By thefe and other experiments often repeated, and made in various ways, and upon other plants, it feems clearly established, that there is no preformation in plants.
According to the theory of Epigenefis, then, the fluids of the male and female are mixed, and an offspring is obtained from these two, which, in form and properties, refembles both father and mother.'
In all vegetable hybrids, some of the features of both parents. are certainly to be recognized, but the male influence seems to predominate in such as we have had an opportunity of examining. The hybrids produced by impregnating the Papaver Somniferum with the farina of the Papaver Orientale, are so very similar to their male parent as scarcely to be distinguished; the only circumstance in which they resemble the female plant, is a slight tendency to produce more flowers than one on a stalk, which the P. somniferum commonly does, but which never takes place in the P. orientale. This circumstance ought to be attended to by those who wish to make improvements by impregnating one plant with the farina of another.,
He gives a very minute account of the diseases of plants, their causes and remedies, which he divides into two classes, external and internal; to some of the latter he has affixed very fanciful names. Medical men will smile to see, Chlorosis, Icterus, and Anasarca, constitute part of the Vegetable Nosology.
When plants become pale from want of light, from defect of nourishment, in bad soil, or from injury received from insects, he terms it Chlorosis. To the natural decay of the leaves in Autumn, he has given the name of Icterus, on account of the yellow colour the leaves assume at that period;-this is very puerile. A similar fanciful analogy has induced him to give the name of Anasarca to the redundant moisture that is perceived in vegetables during wet weather, or in such as have grown in a moister soil than is natural to them. Many of his observations, however, on the diseases of vegetables, and their remedies, are good.
In his History of Plants, he treats of the influence of climate. upon vegetation, of the changes which plants have most probably suffered during the various revolutions this earth has undergone, of their dissemination over the globe, of their migrations, and, lastly, of the manner in which nature has provided for their servation. Many of his observations are intimately connected with certain geological opinions which he entertains, and which he has stated very fully, when speaking of the changes that have taken place in the vegetable kingdom, in consequence of the various revolutions our globe has undergone :- we shall give part of what he says (p. 382.) on this subject.