opportunities of comparison greatly beyond what in ordinary circumstances fall to the lot of an individual. His library, too, was stored with almost every important publication that could be required for his undertaking. With such ample materials, aided by his untiring zeal and the persevering energy of his character, he steadily pursued his allotted task, and only ceased to labour at it when he ceased to live. For some years his health declined, and it is to be feared that the severe and incessant attention which he paid to the elaboration of the great family of Composites had made a deep inroad upon it. As a relaxa tion from his labours he undertook in the last years of his life a long journey, and attended the scientific meeting held at Turin ; but he did not derive from this the antici pated improvement in his health, which gradually failed until his death on the 9th September 1841. Since De Candolle s time various modifications of his system have been introduced by Endlicher, Lindley, Hooker, and
Bentham,In arranging plants according to a natural method, we require to have a thorough knowledge of structural and morphological botany, and hence we find that the advances made in these departments have materially aided the efforts of systematic botanists.
Robert Brown, a Scottish botanist, was the first in this country to support and advocate the natural system of classification. The publication of his Prodromus Floral Novce Hollandice, according to the natural method, led the way to the adoption of that method in the universities and schools of Britain. Sir William (then Dr) Hooker, in his prelections in the University of Glasgow, and in his numerous writings, ably supported Brown. John Lindley also came into the field, and in 1830 published the first edition of his Introduction to the Natural System. Dr Robert Kaye Greville and Dr Walker Arnott were able coadjutors, more especially in the department of Crypto- gamic Botany. From the year 1832 up to 1859 great advances were made in systematic botany, both in Britain and on the continent of Europe. Endlicher s Enchiridion and Genera Plantarum, De Candolle s Prodromus, and Lindley s Vegetable Kingdom became the guides in syste matic botany, according to the natural system.
The following remarks embrace the views of Mr Bentham on the change from the Linnean to the natural system of classification : " The change from the technical to the scientific study of plants was now complete. The Linnean platform, established on the relation of genera and species, had now been so long and so universally adopted as the basis or starting point, that the credit due to its founder was almost forgotten, and it was superseded by the Jussiean method, although it was chiefly by the consistent following out the principles laid down by Linnaeus himself that the change had been effected. Plants were now grouped upon a philosophical study of their affinities, whether morphological, structural, or physiological."
In all classification it is necessary to define what is meant by species. The usual definition of the term has been that a species (as regards the present epoch of the earth s history) is an assemblage of individuals having characters in common, and coming from an original stock or protoplast, and their seeds producing similar individuals. It was also supposed that variation in species was restrained within certain limits, and that varieties had a tendency to revert to the parent form. The view, however, adopted by many now-a-days is, that the tendency to variation is continuous, and that, after a lapse of long periods of time, and under the influence of varying external conditions, the descendants from a common stock may exhibit the differences which characterize distinct species. These are the views which are advanced by Darwin, and which imply a complete revolution in our idea of species. This theory is thus stated by Bentham:—
1. That although the whole of the numerous offspring of an individual plant resemble their parent in all main points, there are slight individual differences.
"2. That among the few who survive for further propagation, the great majority, under ordinary circumstances, are those which most resemble their parent, and thus the Species is continued with out material variation.
3. That there are, however, occasions when certain individuals, with slightly diverging characters, may survive and reproduce races, in which these divergencies are continued even with increased intensity, thus producing Varieties.
4. That in the course of an indefinite number of generations cir cumstances may induce such an increase in this divergency, that some of these new races will no longer readily propagate with each other, and the varieties become New Species, more and more marked as the unaltered or less altered races, descendants of the common parent, have become extinct.
5. That these species have in their turn become the parents of groups of species, that is Genera, Orders, &c., of a higher and higher grade, according to the remoteness of the common parent, and more or less marked, according to the extinction or preservation of unaltered primary, or less altered intermediate, forms.
As there is thus no difference but in degree between a variety and a species, between a species and a genus, between a genus and order, all disputes as to the precise grade to which a group really belongs are vain. It is left in a great measure to the judgment of the systematist, with reference as much to the use to be made of his method as to the actual state of things, how far he should go in dividing and subdividing, and to which of the grades of division and subdivision he shall give the names of Orders, Sub-orders, Tribes, Genera, Subgenera, Sections, Species, Sub-species, Varieties, &c. } with the consequent nomenclature.
Such a systematic arrangement is founded on a hypo thesis which, so far as the present flora of the globe is con cerned, cannot be demonstrated. Conjecture is hazarded as to the present epoch of the earth s history, by extending back to unlimited ages. If the theory is consistent with what we see around us, and is founded on plausible grounds, then we must think that we have ascertained the plan followed by the great Creator, Designer, and Upholder of all things, that we have been able to ascertain and follow His woik- ings, and the mode in which He has created the diverse plants which have covered our globe in time and space. This new phase of systematic botany, however, requires more definite data to lead to its adoption as an explana tion of the plan of creation.
The Physiology of plants did not keep pace with the advance in Classification. Grew and Malpighi were the earliest discoverers in this department of botany. Hales also contributed to it by his observations on the motion of fluids in plants. The subject of fertilization was one which early excited attention.
was entertained in early times, long before separate male and female organs had been demonstrated. The produc tion of Dates in Egypt, by bringing two kinds of flowers into contact, proves that in very remote periods some notions were entertained on the subject. Female Date Palms only were cultivated, and wild ones were brought from the desert in order to fertilize them. Herodotus informs us that the Babylonians knew of old that there were male and female Date-trees, and that the female required the concurrence of the male to become fertile. This fact was also known to the Egyptians, the Phoenicians, and other nations of Asia and Africa. The Babylonians suspended male clusters from wild Dates over the females ; but they seem to have supposed that the fertility thus
produced depended on the presence of small flies among
