II. MESOLEPIDIUM. Scales of the cup middling sized. Matu ration annual or biennial. 1. AIPHYLLUM. Leaves evergreen. a. Ilicinia. Maturation annual. Q. Ilex. b. Phyllodrys. Maturation biennial. Q. Suber, &c. c. Phyllocentron. Maturation biennial; leaves stiff. Q. coccifera, etc. III. MACROLEPIDIUM. Scales of the cup large; leaves falling in autumn; maturation biennial. 1. PACHYPHLONIS. Scales of the cup thick. a. Agilops. Scales flat, usually straight. Q. Græca, &c. b. Egilopsidium. Scales angular; reflected. Q. Vallonea, &c. c. Microægilops. Scales connate, free at their apices only. Q. Persica, &c. 2. STENOPHLONIS. Scales long and straight, cylindrical, thinner towards the tips. a. Sclerodium. Scales stiff. Q. Austriaca. a. Camptolepis. Scales recurved. Q. Castaneafolia. The above arrangement appears to us to be for the most part natural, but judging from the characters given, from the plates, and from the known variability in form, direction, and length, of the scales of acorn-cups, especially in the South of Europe, and remembering that some of the species distinguished by duration of maturation, differ scarcely, if at all, in any other point whatsoever, we cannot but suspect that, to a certian degree, Dr. Kotschy's Groups I., II., III. represent species; his divisions 1, 2, &c., sub-species; his a, c, varieties; and his species specimens. Not altogether so, certainly, but to no inconsiderable degree. Thus, Q. Pedunculata and Q. Robur are ranked as varieties by most authors, including M. A. DeCandolle, who cannot be accused of any too great tendency to unite, yet here they rank under different subordinate groups. Then again we find Dr. Hooker, in the paper above quoted, vouching, from his own personal experience and that of his fellow-traveller Mr. Hanbury-and this after examination in the same localities whence so many of Dr. Kotschy's species were obtained-for the fact of thirteen of Dr. Kotschy's Syrian and Palestine species alone, together with "an N.H.R.-1864. R "equal, or probably a much greater number of the so-called species " of Asia Minor and other parts of the Levant," being referable to the three well-known trees called by old Botanists Q. pseudococcifera, Q. infectoria, and Q. Egilops. Thus the first of these includes 6 Kotschyan species, the second, probably 10, and the third about as many. Of Kotschy's 40 species, no less than 26 are reduced by these observers, most of them with certainty, and all with probability, to 3! Then again, with regard to the annual or biennial maturation of the acorns (a character apparently of high physiological importance, but which, like so many other apparently inviolable diagnostic marks, may depend on very ephemeral and changeable causes); Kotschy, in his tabular arrangement, ranks Q. Ilex in the annual division, but under the species he describes it as biennial; the latter, we should have been inclined to attribute to a misprint were it not that in the course of investigating the subject, we find that J. Gay not only puts Q. Ilex into the annual section, but puts there with it Q. Suber, which Kotschy places in a perennial section! Thus we have a difference, not in opinion, but in a matter of fact, between the two highest authorities on the Oaks (and two of the greatest speciesmakers of the day), about Q. Suber, a Linnæan plant, one of the best known trees in Europe, and one of the longest in cultivation. To add to the confusion, J. Gay, while insisting that the Linnæan Q. Suber consists of two species, one, Q. Suber, of annual maturation, the other, Q. occidentalis, of biennial, does not hesitate to assert that Q. Ilex, Q. Ballota, and Q. Suber may be all varieties of one species! This is indeed "straining at a gnat and swallowing a camel." Before dismissing this subject, we may state that we have it as the opinion of an eminent Portuguese Botanist and traveller, that the maturation of the acorns of Q. Suber is annual or biennial according to situation or exposure. It remains for us to observe that the descriptions are carefully drawn up, but that they are descriptions of specimens, not even of varieties, still less of species: no synonyms, no diagnostic characters, no citations of authors, localities, or of Herbaria, except the most meagre, are given; and most wonderful of all to relate, these 40 species, though some of them have been known to science and commerce for upwards of a century, have not-so far as anything this author states would lead us to suppose-given rise to either a variety or a synonym! As a specimen of scientific investigation, therefore, Kotschy's magnificent folio has no recognizable position; it is, however, a splendid work, its faithful pictures and descriptions have their use; and it is no small merit to author and publisher to have carried it out apparently without any Government assistance. XXXV--THE PARASITISM OF THE MISTLETOE. By ON THE PARASITISM OF THE MISTLETOE (Viscum album). John Harley, M.D. Linnean Transactions, Vol. xxiv. 175. DR. HARLEY'S paper "professes to be an investigation into the anatomical relations of the Mistletoe to the plants upon which it grows, and a deduction therefrom of the general physiological relations existing between them." It would certainly appear that some such investigation was greatly needed, for Dr. Harley says: : "The observations of our own authors in particular (upon the anatomical and physiological relations of the parasite to its prey) are most fragmentary and superficial; and the English student, if he wanted definite information respecting the nature of the parasitism of the Mistletoe, would seek in vain for that information in our own language; and, what is still more remarkable, the subject has never been illustrated by our own botanists. Our fellow-labourers in Germany have, however, advanced our knowledge of the subject very considerably, but yet their observations are incomplete and sometimes contradictory; and, as I have found them in some essential particulars, at variance with my own observations, I have thought it desirable that a subject so important to vegetable physiology as the nature of the parasitism of the Mistletoe should be more fully considered." The botanists who have directed their attention to the parasitism of the Mistletoe,-viz. Henslow, Griffith, Unger, Schacht, and Pitra "all agree," Dr. Harley states Iso far as their individual statements extend, in the following particulars :The young plant first sends into the bark of the nourishing plant a single root, sucker or senker, which, pressing inwards, comes into perpendicular relation to the wood of the nourishing plant, in the cambial layer of which the point rests, and then ceases to grow. In its passage towards the wood, it gives off several horizontal or side roots, which run along the branch in the bark or upon the surface of the wood. These side roots give origin to perpendicular suckers (senker), which come into contact, like the original root, with the surface of the wood. The wood and bark of the mother plant, in their periodical increase, form layers around the suckers, which grow in exactly the same manner in the cambial stratum,' (Pitra, Bot. Zeit. 1861, p. 61), and thus the hardened suckers come to be imbedded in the body of the wood." Through some mistake senker is here rendered by the word sucker. It is not important, unless it lead the reader unacquainted with German to imagine that they who have employed the term meant to imply that the root-like developments thus denominate perform some suctional function. Dr. Harley goes on at once to detail the results of his own observations, which, though evidently made with scrupulous care, and described in great detail, do not include any original notice of the early stages of development of the germinating parasite. We cannot imagine that the most important question at issue amongst writers upon the subject with regard to the relations of the Mistletoe to its nourishing plant, can be satisfactorily settled until the development of the parasite has been traced again step by step. There is no insuperable difficulty in the way of supplying the essential evidence which the observation of development alone can give, and we must beg Dr. Harley not to content himself by letting matters rest where they are now left. We must not, however, underrate the value of the investigations which he here records. So far as they go, they appear to us to be very valuable, and we regard them as wholly trustworthy, with but very small exceptions, which we ascribe to Dr. Harley's having been less familiar, probably, with vegetable than with animal anatomy at the time he undertook this inquiry. There are some little details of stem-structure in which he is widely at variance with M. Decaisne. We must, however, leave this distinguished botanist to look to this himself. Dr. Harley does not give any figure of the wood-structure of the Mistletoe remote from the disturbed tissues characteristic of its thickened attachment, and we scarcely agree with him that an "examination of the woody base and roots of the Viscum, at their junction with the wood of the nourishing plant," is the most likely thing to furnish the clearest demonstration that his view of the homologies of the systems of the wood is correct. With regard to these systems it is not necessary that we should refer to them here in detail. We do not, however, wish it to be understood that we call Dr. Harley's opinion upon them in question. Upon the important question as to whether or not the root-processes of the Mistletoe actually penetrate the wood of the stock, or simply, by being applied against it, become gradually buried in it, just as would be the case with a nail driven through the bark a short way into the wood of the trunk of a living oak, Dr. Harley does not clearly express himself; though, upon an examination of his remarks, we find that he holds an opinion opposed to that explicitly stated by Schacht (an industrious and original, but perhaps not always most accurate observer) viz.-that the root-processes do actually penetrate the stock via the medullary rays. He says "the intrusion of roots of various size and length throws the rays into simple curves or undulations." But the examination of a full-grown Mistletoe is by no means the best adapted to settle this curious point. 66 Some interesting observations are recorded upon the "ultimate anatomical relation" existing between the Mistletoe and its prey. Dr. Harley finds that the vascular systems of the two plants do not directly inosculate, as is represented by Unger." They are, moreover, “arranged at right angles to each other." The presence or absence of a root-sheath to the extremities of the young lateral ramifications of the base of the Mistletoe should be further investigated. Dr. Harley has been unable to find any root-sheath, as Schacht describes. Schacht says, however, in another passage in his 'Lehrbuch,' that the radicular extremity of the germinating axis, though destitute of a proper root-sheath, is provided with a small-celled tissue, which covers the punctum vegetationis of the root, and which replaces the root-sheath. It is possible, therefore, that different conditions obtain in early or later stages of development. From the relation of the 'roots,' to the medullary rays of the nourishing plant, Dr. Harley was led to inquire into the size, number, &c. of the rays of some 30 trees of different species, liable to be attacked by the Mistletoe, with a view to ascertain how far the size and number of the rays might be regarded as determining the relative frequency of the attacks. He gives measurements of the average size of the rays of these species, noting both their depth or vertical extension, and width. The species are tabulated in the order of the size and number of their medullary rays, beginning with those in which they are largest. He finds that the order in which the Mistletoe-bearing species occur in this series "corresponds closely to the relative frequency of the attachment of the parasite to them." The apparent exceptions are attributed to two causes:-1st. "the precariousness of the dissemination of Viscum, the only means for effecting the process being extrinsical and accidental;" and, 2nd, "the nature of the bark, but especially of its periderm." We must here observe that medullary rays are apt to be very variable in their vertical extension, though probably they may be tolerably constant in width. Dr. Harley ought to have stated, in giving the dimensions of the medullary rays of the common Oak, that the small rays only |