pitres 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 Goatsuckers, 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 (Turdida) 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 clas

sification 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 CUCUMBER PLANTS.

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

oles and ramifying in the veins of the leaves. It seems to follow from this that whatever be the path of the water current in the stem itself, it can enter the body of the plant in quantities sufficient for transpiration purposes only along the pathway of the spirals, and can reach the leaves only through the same channels.

The pitted vessels are probably sometimes nearly full of water, and at other times nearly empty, the amount depending on the quantity in the soil and on the activity of transpiration. Owing to the number of very thin places or actual perforations in their walls, they undoubtedly contain air at all times and probably often in large quantities. I regard these vessels as water reservoirs. In this capacity they appear to be admirably adapted to serve the needs of a class of plants which (on account of the extent and unprotected nature of their transpiring surface) often make sudden and very large demands on the stem for water,-demands greater than can be met by the immediate activity of the roots. There is, however, nothing against the supposition that when they are not full of water, they may also serve as aerating organs, the stems being alive and chlorophyll-bearing clear to the center. The function of the spiral vessels, according to my conception, is quite different. They also contain a greater or lesser quantity of water, according to the activity of transpiration and the amount procurable from the soil or from the neighboring reservoirs (the pitted vessels), but unlike the pitted vessels, they are surrounded by a living, non-lignified, nonlacunose parenchyma, and there is no free access of air to their interior, but, on the contrary, so far as we can judge from the anatomical structure, this part of the plant has been developed with special reference to keeping it out. When the spirals are not full of water, they probably contain rarefied air. The very thin walls of these spiral vessels bear on their inner face lignified annular or spiral thickenings, which are probably of great service in strengthening the delicate walls, so that they may be strong enough to resist the collapsing tendency of the vacuum pull due to the osmotic pressure, and yet remain thin enough to readily allow water to filter into

them or out, as the case may be. Such, roughly sketched, is the nature of the bundle, the xylem part of which contains 5 or 6 spirals and from 12 to 15, or more pitted vessels. The cucumber stem, exclusive of the hypocotyle, usually contains 9 such bundles, the 5 larger ones forming an interrupted ring or cylinder in the central part of the stem, and the four smaller ones alternating with the larger ones nearer the surface of the stem, the fifth bundle of the outer series being usually wanting in this species. These bundles are separated from each other by thin-walled, living cells which are nearly iso-diametric. The central portion of this parenchyma and that between the bundles, may be designated as medullary tissue, and that farther out as cortical parenchyma, although all of this fundamental tissue bears chlorophyll, and is used to store starch in prior to the development of the fruit. Outside of the bundles, and not far from the surface of the stem, is a compact tissue formed of numerous elongated, thick-walled, flexible, strengthening cells. These are the bast fibres, forming collectively, the stereomatic sheath. This sheath is several rows of cells thick and forms an broken or nearly unbroken cylinder in the young stem, but is afterwards ruptured longitudinally into a dozen or more strands by the growth of the stem in thickness. Between these strands of stereome, the cortical parenchyma finds its way to the epidermis, except where the latter is specially strengthened by sub-epidermal strands of collenchyma. The stem appears to have so developed as to secure every advantage to be derived from a combination of lightness with flexibility and strength.

To indicate the movement of the water in the stems and leaves, various aniline stains were tried, e. g., eosine, soluble nigrosene, methyl green, methyl orange, acid fuchsin, etc. Eosine proved by far the most satisfactory, none of the other stains moving with anything like the same rapidity, and some of them causing copious precipitates in the vessels. None of the substances in the sap of the cucumber vessels cause any precipitate with eosine, and it is probable that dilute solutions of this substance, while clearly poisonous to the plant, move with the same rapidity as pure water, at least at first.