Imatges de pÓgina

and forthwith closely invested them. As this process went on, a great change was observable in the gonidia; they enlarged, and the chlorophyll acquired a brighter green colour, so that at last they were undistinguishable from the ordinary gonidia of the adult plant. Thus the growth of the hyphæ and the multiplication of the gonidia went on until a complete plant was developed, and this produced spores in the usual way, so that the whole life-history was successfully traced.

It will at once be seen that the significance of these researches does not rest merely on the fact of the actual independence of the two elements of the lichen, but on the proof of the advantages accruing to the algal host from the presence of its parasite. The former, it is shown, does not acquire its full size and activity until it is invested by the filaments of the latter. The benefits afforded by its gonidia to the fungus, again, are manifest; the latter is enabled by their means to live in situations from which it is quite impossible to obtain the ordinary materials of fungoid sustenance, and so has an advantage in the struggle for existence denied to all other members of its class.

The crown of these researches is, however, the discovery of the sexual process. It has long been known that the receptacle of the discomycetous fungi, so similar in many respects to that of lichens, was the outcome of a process of conjugation between two specially modified hyphæ; but all obervers before Stahl failed to find anything of the kind in lichens, although it had been suggested that the spermatia-minute spore-like bodies found in special receptacles (spermogonia) of the thallus-might be quiescent antherozoids analogous to those of the red seaweeds. This conjecture has been shown. by Stahl to be correct. He finds that the formation of the apothecium, or ascus-bearing receptacle, is preceded by the appearance in the substance of the thallus of a twisted filament, the terminal portion of which, becoming straight, grows to the surface, and there projects as a papilla. The coiled portion is called by Stahl the ascogonium, and the straight projecting filament the trichogyne, from its evident resemblance to the body of that name in the Floridea. The whole apparatus constitutes the female organ.

To the trichogyne spermatia were seen to adhere, and there is evidence to show that they actually become fused with it. They are, therefore, antherozoids, and the spermogonia in which they are produced, antheridia. The process of impregnation, thus effected, is followed by a withering of the trichogyne, and by an extensive growth of the ascogonium. Hyphæ are sent out from the latter, and, dilating at their extremities, form the asci of the young apothecium, the remaining tissue of which is due to a special growth of the ordinary hyphæ surrounding the ascogonium, induced indirectly by the sexual process.

Mr. Darwin's exhaustive work on Insectivorous Plants' still left one point unsettled with regard to the extraordinary habits of these carnivorous members of the vegetable kingdom. The complete

adaptation of structure to the function of capturing insects was made. clear enough; there was no doubt that the prey was digested, and digested by a secretion having the properties of the gastric juice of an animal, but it still remained to be shown that the plants were actually benefited by this flesh diet; indeed many observers went so far as to deny altogether that the capture and digestion of insects was of use to the plant, and to look upon the whole process as a purely pathological one.

The evidence thus lacking has been supplied, during the course of the present year, by the researches of Mr. Francis Darwin, who has proved by a series of careful and laborious experiments, that, in the case of Drosera, at any rate, the plant is directly and markedly advantaged by a regular supply of animal food.

Mr. F. Darwin's mode of procedure was as follows. He placed a number of plants in soup-plates, dividing the plants in each plate into two equal divisions by a wooden partition. The plates were placed in a hothouse, and covered with muslin to prevent the access of insects, the capture of which would of course have vitiated the -experiment; in each plate, the plants on one side of the partition were kept without animal food, while those on the other side were fed at frequent intervals with pieces of roast meat of about one-fiftieth of a grain in weight. The experiment was begun on the 12th of June, 1877, on which, as on the following day, the operation of feeding was performed; this was discontinued until the 5th of July, but from that time was continued regularly. By the 15th of July the plants on the fed side were markedly greener than those on the starved side, and a microscopical examination showed that the former contained a far greater amount of chlorophyll, the grains of chlorophyll being loaded with starch. The fed plants were therefore assimilating more rapidly and were laying up more reserve material than the unfed.

On the 5th of August the number of fed was found to be distinctly greater than that of starved plants, in the proportion of 149 to 1100, notwithstanding that the latter were, at the commencement of the experiment, in slight excess in every one of the plates, and were, to all appearance, in a more flourishing condition.

The plants flowered, and by the end of August nearly all the seed capsules were ripe. The flower stems were then cut off, the seeds collected, and the plants themselves in three out of the six plates dried. The two sets were then compared with one another, in respect of their number, size, and weight, the number of capsules produced, the weight of the capsules, and the number and weight of their contained seeds. The results thus obtained are very striking; in one circumstance only-that of the average height of the plants-was the advantage on the side of the unfed specimens, and even then the Journal of the Linnean Society,

3 The Nutrition of Drosera rotundifolia.' Botany, vol. xvii. No. 98, 1878.

proportion was only as 100 to 99.9; in every other respect they were completely outstripped by those supplied with ready-made nitrogenous food. One very interesting point is, as Mr. Darwin remarks, that the difference is most marked in all those structures relating to reproduction: thus while the proportion between the average weights of the starved and fed plants is as 100 to 141.3, and that between the total number of stems as 100 to 169.9, the total calculated number of seeds yielded by all the plants was as 100 to 241-5, and the total. calculated weight of the seeds as 100 to 379-7. Thus the very remarkable result is arrived at that, with equal numbers of unfed and fed plants, the latter were enabled to produce nearly two and a half times as many seeds, and nearly four times as great a weight of seeds, as the former, by being supplied with a quantity of animal food so.small that each plant could not have had more than a few grains during the whole time the experiment lasted.

After the removal of their flower stalks, the plants in three of the plates were allowed to rest during the winter in a hothouse, and were once more examined in the spring. It was then found that the rootstocks on the fed sides were visibly larger than those on the starved sides, and that this betokened the storing up of a greater quantity of food material was shown by the fact that while the number of starved to that of fed plants was as 100 to 108, the proportion between their average weights was as 100 to 213, and that between their total weights 100 to 251-6. Thus, although the fed plants had consumed so much more substance in the production of an increased quantity of larger seeds, they had yet been able to lay up so great a store of reserve material as to come up the next spring, each more than twice as heavy as similar plants kept without animal food, but otherwise under precisely similar conditions.

In a postscript to his paper, Mr. F. Darwin states that researches. resembling his own in all essential respects have been carried out in Germany by MM. Reiss, Kellerman, and von Raumer, the chief difference between their experiments and his being that they fed their plants with aphides instead of with roast meat. The results obtained are quite in agreement with those of Mr. Darwin, and thus furnish an independent proof of the fact, that, so far from its being impossible for plants to assimilate previously elaborated protoplasm instead of building it up from simple inorganic compounds, they may and do take in nitrogenous food in that complex form, and profit by the change to such an extent as to produce more and larger seeds, and to lay up greater quantities of reserve material for the next season's growth.

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The study of the carnivorous plant' has shown how similar are the digestive processes in the higher members of the vegetable kingdom to those of animals: a recent research by Professor von Naegeli "

Ueber die chemische Zusammensetzung der Hefe.' Sitzungsberichte der math.phys. Classe der k. k. Akad. der Wissenschaften zu Münch, 1878, Heft 2.

extends the similarity to one of the lowest of Protophytes—the yeastplant, and shows, further, the closest analogy between the two great groups of living things in respect of another important function, that of excretion. Naegeli's analyses of yeast show that, besides the albuminoids of which the contents of the cells are mainly composed, there always exist about two per cent. of peptone, a substance hitherto only known in animals as a result of the digestion of protoids. The peptone in yeast exists, moreover, under the three modifications (a-, b-, and cpeptones of Meissner) which have been taken to represent as many stages in the digestion of proteids in the stomach of a mammal.

It has long been known that, in plants as in animals, the giving off of carbonic acid, as a product of tissue-waste, was a necessary concomitant of life; but respecting the nature of the nitrogenous products of oxidation, the existence of which, reasoning from analogy, was quite as certain as that of carbonic acid, little or nothing was ascertained. But Naegeli's results show that besides the glycerine and succinic acid known to exist as 'extractives' in yeast, there are also leucin, guanin, xanthin, and sarkin, all of which are well known as nitrogenous products of the waste of animal tissue, many of them being normal constituents of the urinary secretion of the lower animals, while one-leucin-is, there is reason to believe, an intermediate stage in the formation of urea, the most important constituent of the urine of mammals.

In connection with this subject some observations of M. Miquel on the means of dispersal of yeast, and presumably also of other minute organisms, may be mentioned. M. Miquel exposed to the air in the wine country of the south of France, in the month of September, vessels containing sterilised grape-juice, and he found that, in every case, spontaneous fermentation took place, provided that the vessels were uncovered, but that if a covering of fine gauze was placed over them only a comparatively small number fermented, the remainder becoming mouldy. He attributes this fact to the free access, in the former case, of gnats carrying yeast-cells on their proboscides from the vineyards. If this be true-and there seems little reason to doubt it -it furnishes us with an interesting case of the transport of infectious matter by insects.

An argument for the doctrine of contagium vivum is afforded by the instructive history of an epidemic of typhus which took place last year in the barracks at Tübingen.8 The barracks are constructed to hold two companies in each wing, and it was observed that the forty-eight men who fell ill belonged, without exception, to the two companies -the 9th and 10th-inhabiting the eastern wing of the building, to 'De la présence dans l'air du ferment alcoolique.' Comptes-Rendus, Nov. 11, 1878.

• Dotter, Eine Typhusepidemie in der Kaserne zu Tübingen in Januar, &c. 1877. Centralblatt f. d. med. Wiss., 1878, No. 40.

which part the disease was exclusively confined. There seemed to beno possibility of infection from without, and such causes as improper food, bad air, exhaustion, or cold, would have affected all the soldiersequally. Attention was, therefore, directed to the water supply, and it was found that there were four springs for the whole building, one of which was used exclusively by the 9th and by the eastern half of the 10th Company. Of the twenty-five cases of illness in the latter Company, no less than twenty-one belonged to its eastern half, so that forty-five out of the whole forty-eight cases were of men who had used the water of this particular spring. A further inquiry showed that in the immediate neighbourhood of this spring, was a pit full of vegetable débris, known to have formerly been a stagnant. pool; the shaft dug for the spring in question was found, by samples of earth taken from it, to be very rich in organic constituents, and the water of the spring itself was remarkably rich in living organisms.

In the first number of this Review we drew attention to Mr. F. Day's observations on certain amphibious fishes of India. Similar observations have recently been made on South American fishes, by M. Jobert," who has recorded some very remarkable facts. We mentioned that in Ophiocephalus, the air-breathing organs consist of a pair of offshoots from the pharynx, quite independent of the airbladder, so that the true homologue of the lung of the higher vertebrates, itself serving only as a float, coexists along with special dilata-tions of the alimentary canal, to which the actual functions of a lung were assigned. It has always been thought, indeed, that in noTeleostean fish did the air-bladder take on a respiratory function, but that in every case, where the habits of the animal rendered the direct breathing of air a necessity, some other portion of the digestive tract was modified for the purpose.

Jobert has, however, re-examined some rather doubtful cases, and has come to the conclusion that in at least three bony fishes, namely,. Erythrinus brasiliensis, E. tœniatus, and Sudis gigas, the swimbladder is physiologically, as well as morphologically, a lung. In the two first-named species the bladder is divided into two compartments, the anterior part of the hindermost of which is very abundantly supplied with blood-vessels, derived not only from the usual branch of the aorta, but from a special vein bringing venous blood from the intestine, and even from the walls of the abdomen. After circulating through the rich plexus of blood-vessels in the air-bladder, the blood is returned in a purified state directly to the sinus venosus or hindmost division of the heart, instead of being taken into the portal vein, as is usually the case with the returning current from the swim-bladder. It is a remarkable circumstance that a third species.

Recherches pour servir à l'histoire de la respiration chez les Poissons.' Ann. des Sci. Nat., Zool., t. v. (1877) and t. vii. (1878).

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