« AnteriorContinuar »
aims of ornithology is to establish the true relations of existing and extinct forms of birds to each other, and to other groups of animals that are either to be found living at the present time, or else have existed during past ages of the earth's history. In other words, the true classification of birds is to be sought for, and ornithology in this sees its most difficult problem and its final goal.
But the knowledge of the origin of this most perplexing group of vertebrates, their evolution, and our power to correctly classify them can only come to us in one way, and that is through a complete understanding of their structure, and a comprehension of the anatomy of those groups more or less nearly related to them. Other departments, however, can lend great assistance here, and the avian taxonomist can have much light thrown upon his arduous task through the revelations of researches in the fields of physiology, of geographical distribution, nidology, paleontology, and other biological sciences.
With these facts before us, it is with no little interest that the taxonomist scans the pages of the second edition of “The A. 0. U. Check-List of North American Birds," with the view of ascertaining what evidences there may be in the direction of a better knowledge of the classification of our birds. There may have been some excuse for the numerous symptoms of the somewhat antiquated taxonomy that characterized the arrangement of North American birds in the 1886 edition of the A. O. U. Check-List, but not so this last one, provided we find that the earlier classification has been retained. For, be it known, in the meantime, that is, from 1886 to 1895, the avian morphologists had not been idle. There were very many useful sug. gestions in the admirable work done by Dr. Stejneger that appeared shortly before the 1886 edition was printed. This was followed, in 1888, by the superb volumes of Fürbringer, with one of the most elaborate classifications of birds the world has ever seen ; Seebohm, of England, had done a great deal, while the present writer had published accounts of the osteology of nearly every family of N. American Birds, and Mr. Lucas stands prominent in his excellent anatomical work upon many of the groups. English pens had contributed memoir after memoir along similar lines, and one has but to turn to the essays and volumes of Newton, Gadow, Beddard, T. J. Parker, Sharpe and many others to appreciate this. But for one to fully know what a deal was done during the nine years I speak of, it is but necessary to read the enthusiastic address of Fürbringer given before the Section for the Anatomy of Birds at the Second International Ornithological Congress, held at Budapesth in 1891. A powerful light has been thrown upon the structure and affinities of the various groups of birds, and has it in any way affected the classification of the 1895 CheckList of North Ameican Birds, that is, in so far as the main groups are concerned ? Not in the least. Apart from the addition to the List of the family Cotingida, the taxonomy of the orders and families as given in 1886 are identical with the arrangement reproposed in 1895. For example, we still find the Grebes, Loons and Auks retained together in the Order PyroPODES, with the first-named separated from the last two by subordinal lines; whereas, Fürbringer, Thompson, Sharpe, myself and others, all of whom have examined the structure of these birds, have shown the affinity existing between the Grebes and Loons, and that these two families are very distinct from the Auks. The Auks, in fact, occupy a group by themselves, and are more nearly related to the Longipennes. Fürbringer separated them very widely from the Grebes and Loons, in which opinion Sharpe and others concur. That the Longipennes and the Limicolæ are akin is now generally recognized by those who have studied the anatomical structure of the members of the two groups, yet in the A. O. U. classification, six entire Orders stand between the Gulls and the limicoline assemblage. Fürbringer makes a “Gens” Laro-Limicolæ, and Sharpe keeps the two groups close together. As long ago as 1867 Professor Huxley clearly showed the osteological agreement between the skull of a Plover and that of a Gull.
That the Fowls (Gallina), Pigeons (Columbæ), Raptorial Birds (Accipitres), Parrots (Psittaci) and the Cuckoos (Coccyges) as groups should stand in lineal series I can well believe-but as Gadow, Hubert Lyman Clark, myself and others have frequently pointed out, the Owls do not belong with the Accipitres or the Falcons and their kin, while I make separate groups for the Cuckoos, Kingfishers and Trogons. The Woodpeckers are not separated from the Passeres by the Goatsụckers, Swifts, and Hummingbirds, as the A. O. U. List now have them arranged, but the Woodpeckers, in the list of North American Birds, taxonomically arrayed, should stand immediately next to the Passeres, while the “Macrochires" is a thoroughly unnatural group, inasmuch as birds are no longer classified and restricted to groups on account of their having long pinions.
Finally we come to the Passeres with the lineal arrangement of the 21 families composing the group. Now, as a classificatory scheme, this lineal method of showing it is unsatisfactory in the extreme, but it appears to be the only available one to adopt in the Lists in books. A.“tree” shows what is meant much better and truer, but it can never form a part of a List. Still these Lists show something, for we can, among other things, indicate in them the families that should, in our opinions, occupy the extremes—as, for instance, the Tyrannidæ and the Corvida, but in numerous cases it will be found to be exceedingly difficult to complete the sequence, even to carry out the hopes of the classifier. However, marked violences can usually be avoided, and marked affinities often shown in a classification of this kind.
The scheme adapted in the A. O. U. Check-List, although not altogether a bad one, is capable of showing a more truthful arrangement of the families of passerine birds. In the first place, this List should be completely reversed; then the Thrushes (Turdidæ) placed more nearly where they belong; and the Laniidæ removed very much nearer the Clamatorial end of the sequence, and away from the Vireos, with which family they have no special affinity. Thus much for the progress in American ornithology during the past ten years; our ornis has been most carefully studied in so far as the identification of new species and subspecies is concerned, but the matter of scientific classification of birds demands increased attention, and it is to be hoped that a greater number of avian morphologists will arise, and should that come about, the classification of the next edition of the A. O. U. Check-List will, in truth, be archaic if again printed without change; the 1895 one, just out, is a number of years behind the science of the times, so we may easily imagine how very backward it will appear ten years hence.
THE PATH OF THE WATER CURRENT IN CUCUM
BY ERWIN F. SMITH.
Although Sachs' notion that the ascending water current in plants passes through the walls of the vessels and not through their interior, was rendered very doubtful long ago, if not thoroughly exploded, by the experiments of Elfving, Vesque, Erera, Boehm and others, the old statement still remains in many of the text books and continues to be taught. For this reason, and because the papers of the opponents of this view do not seem to have received much attention in this country, while Dr. Sachs' Lectures on the Physiology of Plants in H. Marshall Ward's admirable translation, is known and read everywhere and deservedly so, it may be worth while to call attention once more to the present state of our knowledge on this subject. This I shall do by presenting some experiments of my own, which were made a year ago on Cucumis sativus L. These were undertaken partly to verify some of Strasburger's statements in his book Ueber den Bau und die Verrichtungen der Leitungsbahnen in den Pflanzen, and partly to determine, as accurately as possible, the path of the water current in Cucurbitaceous stems, subject to the attack of Bacillus tracheiphilus. They were begun about March 20, and continued till some time in April, the weather being by turns warm and cold, sunny, windy, cloudy and rainy. About 30 well grown cucumber vines were experimented upon, the following being selected as typical. All were under glass in a large hot-house, devoted to the cultivation of cucumbers for the winter market. None of the vines trailed on the ground, but all were trained up on stakes or over high strung wires. A sharp razor was used in cutting the stems.
Before proceeding to the experiments, it will be necessary for the sake of those who are not familiar with the structure of the cucumber stem, to briefly indicate its anatomy. The bundles are bi-collateral, i. e., there is a group of phloem on the inner, as well as on the outer face of the bundle. The outer phloem is separated from the central strand of xylem by a cambium zone, which is restricted to the bundle, i. e., not inter-fascicular. The inner phloem is separated from the xylem, by a meristematic tissue structurally much like cambium, but functionally different. The phloem consists of numerous large sieve tubes, with the usual accompanying cells and cambiform cells. The central or xylem strand of the bundle consists principally of large pitted vessels, held together by shorter tracheids and lignified parenchyma. The mode of origin of the pitted vessels, i.e., out of a series of large superposed cells, is plainly visible, the cross septa being sometimes present and perfect, but more often partially wanting or reduced to mere rims on the inside of a continuous tube. The walls of these tubes contain thousands of very thin places, or actual perforations, (in many cases the central slit takes no stain), and the tubes appear to be admirably adapted for water reservoirs, any adjacent portion of the plant being clearly able to draw from them without hindrance. It appears to me somewhat doubtful, whether they also function as direct water carriers. This business seems more suited to the spiral vessels which occur in a little group on the inner face of the xylem strand, embedded in a delicate, non-lignified living parenchyma, which frequently contains chlorophyll. The walls of these spirals are not pitted; their bore is almost capillary, i. e., much less than that of the pitted vessels; and they are of great length, probably by means of splicings extending as open tubes the whole length of the vine. That they are of more fundamental importance to the plant than are the pitted vessels, appears from the fact, that they are the only tubular parts of the xylem to be found in the smaller roots, and are also the only xylem-vessels passing out of the stems into the peti