Page:Transactions NZ Institute Volume 19.djvu/385

 "(a.)

Also, p. 209:—

"(e.) Among the Myoporeæ, the species of Myoporum have numerous round oil-cavities of unequal size in the leaves and the outer cortex of the branches. The cavities are superficial and separated only by 1–2 layers of cells from the epidermis, which is arched convexly outwards; e.g., M. parvifolium. In M. tuberculatum, on the contrary, according to Unger, they occur in the middle of the chlorophyll parenchyma of the leaf. They are surrounded by 1–3 layers of flattened cells. As far as investigated, their origin appears to be lysigenetic."

Observations.—I made observations on the leaf and stem of M. lætum through the autumn and winter, examining sections through fresh specimens and specimens preserved in alcohol, with the following results:—

In a piece of mature leaf, $4⁄25$ths of a square inch, there were 164 glands. This gives 1,025 to the square inch, so that about 1,000 to the square inch appears to be a fair average of their number. They are, however, much fewer towards the base of the leaf, near the insertion of the petiole on the stem, but are not altogether absent. In the lamina they occur both in the parenchymatous tissue and also in the midrib (see fig. 4), and are entirely surrounded by two or three layers of compressed colourless cells (see figs. 1 and 2).

The upper epidermis is often arched outwards over the glands (see fig. 1), but there are always at least two rows of cells between the epidermis and the compressed cells surrounding the gland, one of the rows being palisade cells. The cells of the palisade parenchyma above the gland are also colourless.

The glands vary in size from $1⁄32$–$1⁄16$ inch diameter in the lamina; in the midrib and stem they vary even more, some being found considerably smaller. The shape of the gland is spherical, and in the dried specimen which I examined the contents had all fallen away from the centre, forming a granular colourless coating round the inside of the gland, enclosing a vacuole. In the specimens preserved in alcohol, the contents had coagulated into little brownish-yellow masses, apparently of gum. (See fig. 2.)

In very young leaves there are no glands (see fig. 5), but they begin to appear when 10 or 12 leaves are formed nearer the apex (fig. 6). The rapid growth of the young leaves appears to retard the formation of the glands, but after their first appearance they are soon found in considerable numbers (fig. 6).

In the stem the glands appear both in the pith and cortical parenchyma (fig. 7). Their occurrence in the pith is not mentioned by Hooker or De Bary. They are scattered irregularly