cultivated races. So the seedling mulberries so extensively raised in the south of France under the name of Pourrettes, as stocks for budding the large-leaved cultivated sorts, although the seed is generally taken from the latter, produce for the most part individuals so inferior in foliage, as to be rarely kept for use without budding.

In the case of shorter-lived plants, we cannot either take for granted the above quoted assumption, that our drum-cabbages and cauliflowers "never return to any of those wild species so different in habit, which grow on the cliffs of the Ocean and the Mediterranean." Our own observation of the peculiar circumstances under which we have usually seen the wild cabbage on the cliffs of the Channel, would lead us on the contrary to conclude that they are all descendants from self-sown cultivated varieties. We admit that they may not be precisely similar to the truly indigenous forms now very rare in the southern Mediterranean region, but they are nearer to them than to what we suppose to be their plethoric ancestors; so near, indeed, as that few botanists would distinguish them. It is well known, also, that in certain soils, with careless treatment, Cauliflowers, Brussels sprouts, etc., tend very much to lose their respective deformities, whilst they retain them through any number of generations in genial circumstances. We believe, also, that a similar return to a normal reduced, but healthy and hardy condition, after some generations, is frequently exemplified in the Carrot, the Parsley, the Lettuce, and several others. At any rate, we cannot agree to the positive contrary affirmation without much better proof than has yet been adduced. We must add, however, that our remarks apply only to races produced by cultivation, the question as to the possibility, under any circumstances, of the reversion of geographical and other wild races to the type they are supposed to have been derived from, is much more problematical, but is not touched upon in the Memoir before us.

An observation of some interest, if it really be founded upon satisfactory statistical data, is that the species in which this very great variation of the fruit has been observed, such as Pears, Cucurbitaceæ, etc., have all an inferior fruit-which, with some modern botanists M. Decaisne explains as being formed by a receptacle, (not the calyx), in which the ovaries are immersed. "L'adhérence de l'ovaire," he adds, "serait donc l'état organographique qui se prêterait le mieux à la variabilité du fruit. Ce que nous savons des Ombelli

fères, des Cupulifères et des genres Néflier et Rosier, chez lesquels le fruit est partiellement infère, n'affaiblit certainement par cette manière de voir." If the fruits of Umbelliferæ are really as variable as they are thus supposed to be, the principles upon which that difficult Order is usually divided into genera and species will require great modification. And if our cultivated plums are all conspecific with the damson, the bullace, and the sloe, and our peaches and nectarines with the almond, these superior fruits will surely not yield in variability to any of the inferior ones experimented upon by M. Decaisne.

M. Decaisne notices the popular belief, that certain varieties of fruit trees degenerate and decay in consequence of constant propagation by grafting, only to protest against it as a vulgar error, founded partly on the evident results of improper cultivation in suitable soils, or on the neglect of old varieties for new ones, and fostered in some measure by interested motives on the part of raisers of new fruits. We believe that the most eminent of our own Horticultural physiologists are disposed to agree on this subject with M. Decaisne, but we think it a question well worthy of further study on the part of so careful a philosophical observer. M. Laujoulet in the above quoted paper in the Revue Horticole, is in direct opposition to him. And if, as is shown by Mr. Darwin, constant in-breeding in plants, without cross fertilisation by other individuals, weakens the constitution, and especially hinders the production of good seed, there seems to be no physiological reason against a gradual weakening of constitution in the course of a number of generations, if they may be so termed, of buds, without an occasional renewal by seed.

XI.-AGARDH'S SPECIES ALGARUM.

SPECIES, GENERA ET ORDINES ALGARUM: auctore J. G. Agardh, Vol. 2, Pars III. Lundæ, 1863.

AFTER a lapse of ten years, Professor Agardh has resumed the publication of his Species Algarum, and in the present part brought the subject to the end of the Florideæ, or Rhodospermatous Series.

The whole of the concluding fasciculus,-itself almost a volume, having 492 pages,-is occupied with the family Rhodomeles, the

most extensive of the "Orders" of Florideæ, and also the most varied in external modifications of the frond, and the highest in the structure of the fruit. If there be any direct passage from the Alga to the Hepatica, it will probably be found in some Rhodomelous form. Not only does the external aspect of some, as of Leveillea Schimperi, Dne. (Polyzonia jungermannioides, Mart. and Her.) closely simulate in foliage and mode of growth some Jungermannia; but it is also in this Family that Florides are found adapting themselves to fresh water, and even creeping on shore, and mixing with mosses under trees. More than one species of Bostrychia, whose British representative is found in brackish water, affects fresh water streams; and Agardh enumerates among the varieties of his B. tenella the "B. terrestris,” Harv., which was found growing among mosses and phænogams on the beach of the Friendly Islands, above high water mark, and assuming the densely tufted, cushion-like growth of a Jungermannia. This terrestrial growth is the more remarkable because the majority of the Rhodomeleæ only grow in deep water, or at least on the darkest side of deep rock pools.

Professor Agardh distributes the Rhodomeleæ into 33 genera, which he groups under seven tribes. Of the genera, three-namely, Neurymenia (founded on Fucus fraxinifolius, Mert.); Placophora (Amansia Binderi, J. Ag., and A. marchantioides, Hook. f. and Harv.), and Tanioma (Polysiphonia perpusilla, J. Ag.)—are proposed for the first time. The largest genus is Polysiphonia, of which 119 species, known to the author, are fully described, while no less than 80" species inquirenda” are appended. Besides these, a very considerable number of the reputed 'species' of authors have been reduced, and distributed under known forms. This portion of Professor Agardh's work must have been most troublesome and tedious, and the manner in which it has been accomplished is highly creditable to his skill and discrimination.

The volume throughout bears abundant marks of care and honest application to a difficult task, and most of the changes in nomenclature which are proposed will be readily acquiesced in. We noticed but one proposed change in a generic name which appears to be uncalled for, where Chondria of the elder Agardh, adopted in 1853 for a portion of the original species by Harvey (Ner. Bor. Amer. part 2, p. 19), is now changed into Chondriopsis, J. Ag. M. S. We notice also a most extraordinary omission of all reference to the Flora Novæ Zelandia,' where several new species of Rhodomeleæ are described

and figured. We should have hoped that that work had reached Sweden before now.

One portion of Professor Agardh's task, and perhaps the most difficult one, the Zoospores, or Chlorosperms, remains to be executed. For this, which includes the fresh water Algæ, we believe that considerable preparation has been made, and we venture therefore to look forward to its commencement, at least, before the lapse of another ten years.

XII.-HARTIG'S CONTRIBUTIONS TO VEGETABLE PHYSIOLOGY. CONTRIBUTIONS TO VEGETABLE PHYSIOLOGY. By Dr. Th. Hartig. Botanische Zeitung. 1863.

Dr. HARTIG has been contributing a series of interesting papers to the Botanische Zeitung during the past year upon subjects which have been too little pursued by our own observers, and upon which we greatly need extended and diligent inquiry. At present we confine ourselves to a very brief notice of the subjects treated of. They

are:

1. Upon the Exhalation of Vapour from twigs while destitute of their leaves (p. 261).

Experiments upon the Acacia and Hornbeam show the amount of exhalation to be very unequal at different hours of the day; that it is least between sunset and sunrise, reaching a maximum at mid-day. A comparative table is given, showing the amount of water exhaled in the 24 hours by different species. The quantity exhaled by the Willow and Elm is more than doubled in the Ash and Maple, trebled in the Lime, and quadrupled in Acacia and the Oak; while in the Alder it is nearly twelve times as great as in the two firstnamed.

2. Upon the Movement of Sap in Woody Plants, (pp. 269-277). In 1861 the author reported the result of experiments upon the 'bleeding' of the Hornbeam, with reference particularly to the daily cessation of the flow of sap, which flow was stated to alternate with periods during which the wounds made in the trunk absorbed liquids presented to them. (See Nat. Hist. Review, 1862, p. 439.) As Dr. Hartig's experiments had not then been extended over the entire period during which the tree is liable to bleed, he has since made

some further observations with reference to it. He finds that the alternation of bleeding and absorption does not occur so regularly as at first appeared, and that during the first half of the bleeding season, periods of absorption were either very irregular, or did not occur at all. Owing to the difficulty of securing his manometer in the holes which he had bored in the trunks of the trees experimented upon, so as to be air-tight, he made a number of observations by simply inserting bent, open glass-tubes through corks fastened in the mouth of the holes (which were of equal size), and counting the number of drops which flowed per minute. The amount of absorption could not, of course, be measured, but its commencement was indicated by the return of the fluid in the tubes. The flow per minute, from several trees, is tabulated from the 17th March to the 1st May. From an improved application of a mercurial manometer, Dr. Hartig was enabled, last Spring, to make more exact observations upon the amount of fluid absorbed by the wounds. These observations, also, are tabulated from the 24th March to the 2nd May; the experiments being made upon Hornbeam, Maple, Birch, and Beech. He adds some remarks upon the relations of the periods of flow and absorption, and on the bearing of these phenomena upon the author's hypothesis respecting the part taken in the movement of fluids in trees by the gaseous contents of the cells, the tension of which varies with temperature, &c.*

3. Upon the Endosmotic relations of the Wood-cells of Coniferæ, (p. 285).

From experiments tried upon fragments of fresh and dry wood of the Silver-fir, which is destitute both of ducts and resin-canals, Dr. Hartig concludes that "dry, dead wood possesses endosmotic capability, while fresh, living wood does not." The difference between them he attributes to the presence of air in the wood-cells of the living tissue; a portion of air being applied to one side of the membrane closing the pore-canals of each wood-cell, while fluid is applied to the opposite side of the membrane in the adjacent cell. In dead wood, when wetted, the whole cavity of the cells becomes filled

With regard to these experiments of Dr. Hartig's, it is needful for us to point out that Professor Ratzeburg (Brandenburg Bot. Ver. Verh. 1861-2, p. 353) wholly denies that, in the case of the Hornbeam, there is an alternation of bleeding and absorption, limited to certain daily periods. Dr. Ratzeburg further states that the condition of the atmosphere, as to temperature and humidity, does exercise considerable influence upon the duration and amount of the bleeding, in contradiction to Dr. Hartig's representation that it was without effect.