and vary in size throughout the secondary stems. In the younger wood of the autumn specimens I found them occurring very rarely for the space of two or three nodes, but after that they appeared both in pith and cortex, though few and irregular in size. In the older wood much larger glands are found, but these are also irregularly scattered, and usually among others considerably less in size (fig. 7). They appear to develope very late in the wood, and appear more frequently in the pith. The contents of the glands of the specimens which had been preserved in alcohol had, as in the case of the leaves, coagulated into little brownish-yellow masses, apparently of gum.
My observations on the development of these glands were imperfect, but they seem to point to a lysigenous origin, for the following reasons:—When first the glands appear in the young leaf or stem, they appear as two or three colourless cells. These cells increase in size, and appear to divide repeatedly, until they form a mass of colourless cells of the size of the mature gland (see fig. 8). [This is easily distinguishable from a vein, as the latter consists of an external bundle-sheath enclosing a bundle of thick-walled cells, slightly pear-shaped with the pointed end upwards, the whole being surrounded by chlorophyll cells (see fig. 3)] . The central cells of the colourless mass seem now to become absorbed, leaving two or three rows of flattened cells (colourless) on the outside, surrounding a vacuole with gummy contents. In the glands of the stem I repeatedly noticed ragged cells and portions of cell-walls projecting into the vacuole of the gland, as if the interior cells had been partially absorbed but the absorption had not been completed. Whether this absorption were partial or almost complete, the surrounding colourless layers in the case of a full-sized gland always assumed a spherical outline.
EXPLANATION OF PLATE XX.
Fig. 2. Transverse section through portion of mature leaf preserved in alcohol × 120. Letters as before. Gland shows gummy contents.
Fig. 3. Transverse section through portion of leaf showing vein (v) × 50. The red substance above the vein is some apparently gummy substance, which is very common in the leaves.
Fig. 4. Longitudinal section through midrib (slightly inclined), showing gland (g) × 166.
Fig. 5. Longitudinal section through young bud × 83, showing growing-point, g.p.
Fig. 6. Longitudinal section through young bud × 83, showing young glands, g.
Fig. 7. Transverse section through stem × 25; p, pith; f.v.b, fibro vascular bundles; c, cortex; g, glands.
Fig. 8. Transverse section through leaf × 83, showing young gland, g.
