ture of this subject have been made by Vesque, Weiss, Russow, Petersen, Van Tieghem, Fischer, Scott, Gérard, Hérail, Lignier, Leonhard and Lamounette.

Various views are held by different writers upon the relation between the internal phloem and the other parts of the bundle. Some believe with de Bary that an actual bicollateral condition exists, and that the internal phloem is as much a part of the bundle as the external, and is of similar origin. Others, notably the French botanists Hérail and Lamounette, believe that the internal phloem is independent of the bundle and of different origin.

The following papers have been specially consulted:

Solereder, H.-" Ueber den systematischen Werth der Holzstructur bei den Dicotyledonen," 1885.

Scott and Brebner.—“ On the Anatomy and Histogeny of Strych. nos." Annals of Bot., Vol. III, 1889.

Scott and Brebner.- "On Internal Phloem in the Root and Stem of Dicotyledons." Annals of Bot., Vol. V, 1891.

D. H. Scott." On Some Points in the Anatomy of Ipomœa versicolor." Annals of Bot., Vol. V, 1891.

"

Hérail. Recherches sur l'Anatomie comparée de la Tige des Dicotylédones." Ann. des Sc. Nat. Bot., Sér. VII, T. II, 1885.

Lamounette." Recherches sur l'origine morphologique du Liber Interne." Ann. des Sc. Nat. Bot., Sér. VII, T. XI, 1891.

LITERATURE RELATING TO GELSEMIUM.

Gelsemium sempervirens is commonly known in the Southern States as the "Yellow Jessamine," and is placed in the order Loganiaceae by Solereder, Engler and Prantl and Gray; in the order Apocynaceæ by Baillon, Le Maout and Decaisne,

In the Laboratory Contributions from the Biological Department of the University of Pennsylvania for 1884, J. G. Shoemaker has a few notes on the stem of Gelsemium. He remarks the widening of the medullary rays, and "the tendency of the pith to be penetrated by several plates of large thin-walled cells, which divide the pith more or less perfectly into four portions."

Professor Rothrock, in February, 1885, made a short verbal communication to the Philadelphia Academy of Natural Sciences concerning this stem. His attention was attracted by the fact that the diameter of the pith is greater in a very young twig than in a stem

four times its size. He notes the presence of the four medullary phloem patches, and their encroachment upon the pith area.

A great deal of work has been done upon Gelsemium from a chemical and pharmaceutical standpoint, but its structure and development have not been thoroughly worked out. The root contains an alkaloid gelsemin, which is very poisonous, but is a valuable medicine when taken in proper quantities. The medicinal properties of Gelsemium were accidentally discovered about the middle of this century. An interesting account of the discovery and the primitive method of extracting the poisonous principle from the root is given by William Procter, Jr., in the AMERICAN JOURNAL OF PHARMACY for 1852.

Other records of the investigations upon the alkaloid gelsemin are to be found in later numbers of this JOURNAL, and in the Proceedings of the American Pharmaceutical Association."

HISTOLOGY OF A ONE-YEAR-OLD STEM.

A transverse section, about 1 millimetre in diameter, of an internode at the close of the first year's growth shows the following structure (Fig. 1). Externally are three to four layers of cork, still covered in places by the prominently ridged cuticle; next is the cortex, consisting of a zone of parenchyma four to five cells. deep, rich in protoplasm and containing abundant chlorophyl and starch grains. A ring of large sclerotic cells, which appear in longitudinal section as clear refractive fibres of considerable length, lies on the outer margin of the vascular bundle portion of the stem. The bundle cylinder consists first of a zone of external phloem about six cells deep. Most of the cells are still embryonic, with large nuclei and abundant protoplasm, some few have differentiated into sieve tubes. In longitudinal section the sieve plates can be recognized. The septa are large, transversely placed, and bear either four or three sieve plates with numerous perforations. The cambium layer is clearly defined by its regular brick-shaped cells with large nuclei.

The wood is a broad zone, occupying more than a third of the area of the section, and is traversed radially by the oblong, deeply pitted cells of the medullary rays. A longitudinal section through the wood shows numerous spiral tracheæ in the inner or protoxylem region; external to this are both short and long tracheids,

whose walls are thickened and deeply pitted. Large vessels are numerous in the outer portion of the zone.

On the inner side of the wood lie four large rounded patches of internal phloem extending into the pith. These patches are two to three times broader than the external phloem zone, and consist also of sieve tubes and undifferentiated phloem elements. The inner margins of the phloem patches are bounded by a two-celled layer, which may be termed a phloem sheath (Fig. 1). This is sharply differentiated alike from the adjoining pith cells and from the phloem. A row of somewhat similar but smaller cells separates

the outer margin of the phloem patches from the wood, and immediately internal to this row are the patches of medullary cambium. The cambium cells have the usual brick-like shape, thin walls and large nuclei. The cells of the sheath are rounded and in close contact with each other. They have thickened pitted walls and are conspicuous by their size and the large amount of chlorophyl and starch they contain. The pith cells are much larger, have thin but slightly pitted walls, and a scanty supply of chlorophyl and starch, while the intercellular spaces are larger than those of the phloem sheath. A few short sclerenchymatous or "stone" cells are some

times present. Very early in the life history of the stem death of the pith cells occurs. The cell contents dry up, the pith as a whole shrinks away from the sides and becomes detached from the phloem sheath, but persists as an inert somewhat lignified mass, until its place is usurped by the enlarging phloem patches.

HISTOLOGY OF THE STEM FROM THE SECOND TO THE TENTH YEAR.

In a transverse section of a stem at the end of the second year's growth, the most prominent change is the increased size of the internal phloem patches. Each has pushed farther out into the pith, and as the growth has been greater in the middle than at the sides, the inner margin has a curved outline, with the convexity toward the pith. The formation of new cells from the medullary cambium takes place centrifugally, the newly formed cells lying external to the old. On the inner side of each patch, adjoining the phloem sheath, a dark crescentic mass of partially obliterated tissue is now evident. This is composed of the older sieve tubes that have collapsed and been pushed together by the pressure from the new elements laid down by the active medullary cambium.

The external phloem has increased but little in breadth, in comparison with the internal patches, but the total number of cells and the actual area of the zone is greater than before. Here and there along the border are darker areas, composed of four or five compressed cells, showing that the same crowding and obliteration goes on, although to a less extent than in the internal patches.

or

In older stems the increased size of the internal phloem patches becomes more and more prominent. The masses of crushed tissue "Hornbast" (Fig. 2) are more numerous and broader, the later formed ones lying in concentric layers external to the older masses. Some large phloem parenchyma cells are often present between the crushed masses, for they are better able to resist the crushing process, owing to their greater turgidity. The patches may thus present a stratified appearance from the alternation of the bands of crushed tissue and the scattered parenchyma cells. Each of the four patches usually divides into two parts, so that in the oldest stems eight cone-shaped masses of internal phloem are present. The neighboring patches grow together laterally, while they continue to encroach upon the pith. In the oldest stem examined (Fig. 2), of about twelve years' growth, the internal phloem patches

entirely fill the former pith area, except a very small space in the centre, where a shrunken thread of dead tissue represents all that remains of the pith. The patches by this time are composed almost wholly of "Hornbast." Only a few sieve tubes are distinguishable, and these are more or less distorted. The contrast between the large cells of the phloem sheath and the dark crushed masses is very striking.

The breadth of the external phloem, which, during the first few years, was less than that of the internal patches, increases greatly in older stems. In a six-year-old stem its breadth almost equals that of the patches; in a ten-year-old stem it exceeds them. The same alternation of bands of "Hornbast" with parenchyma cells occurs as in the internal patches, but as the pressure conditions are different here the bands are narrower and less marked. As the growth has been centripetal, the newly formed tissue lies internal to the old.

stems.

The widening of the medullary rays is very noticeable in older The width of a ray at the periphery of the wood is six or eight times greater than at the centre. Elongated cells, that are continuations of the rays, separate the cone-like masses of the external phloem zone,

HISTOLOGY OF A NODAL SECTION.

Near a node the circle of wood and external phloem becomes elliptical, and the patches of internal phloem lie at the ends and sides of the ellipse. The end patches are considerably larger than the side ones and are further divided into a central and lateral portion, the former for the petiole, the latter to remain in the stem. Higher up, the ends of the ellipse curve out more and more, and soon separate from the sides to form the petiolar bundles. Each bundle is accompanied by a portion of the internal phloem, so that at first the petiolar bundle is composed of external phloem, wood and two small masses of internal phloem. Left in the stem are the two long lateral curves of wood and external phloem as before. The two small groups of internal phloem that remained behind at each end now move together to reconstitute the end patches. Above the node the wood reunites into a continuous ring, while at the next node above, the leaf bundles will be given off from the opposite sides of the stem.