much more frequently to an increase of water in the soil. As many as five leaf coverings have been formed during the period from February to August, three of which were induced by irrigation (Cannon, 1905). From these facts it will be appreciated that this plant is a marked desert type, and on this ground it was believed that the study of the stomata and their relation to the loss of water by the plant would be of profit.

Aside from other features which may be at present disregarded the one pertinent to the matter in hand is the anatomical structure of the leaves (fig. 1). They are 0.3 mm. thick, small, obovate in form, 2 to 3 (or 4) cm. long, rather light green, and slightly glaucous. The cuticle is not thick, and, save for the

isolateral structure, the leaves do not at all strikingly suggest the desert type of foliage (plate 2, fig. 3). The chlorenchyma has above and below a relatively thick palisade of, in each case, a single row of deep, columnar cells. Between them lies a spongy chlorenchyma, one-seventh of the total leaf thickness, of rounded cells, with small intercellular spaces.

The epidermis is of a single layer of cells, 30 to 45 micra deep, and of simple tangential outline, the cuticle being more or less readily corrugated from the stomata as a center.* The cuticle is not at all remarkable, since its thickness is no greater than that on the leaf of many mesophytes. A small amount of "bloom" is present, giving a slightly glaucous appearance to the leaf.

FIG. 1.-Transverse section of portion of leaf of
Fouquieria splendens.

The stomata are of very simple character, as seen in fig. 3. The only structural feature which marks it as a supposedly desert type is the somewhat marked outer ridge. There is no inner ridge. When young the dorsal and ventral walls are not markedly thickened, but become very much so with age, and as the secondary thickening proceeds the mobility of the organ is reduced. The lumen, as a result, becomes reduced to a thin space for the inner half of the guard-cells, but remains approximately cylindrical in the outer half. The outer wall remains thin, and by its stretching, when the

*A not uncommon character; e. g., it appears in Ampelopsis.
tInner, i. e., adjacent to the pore; outer, adjacent to the epidermis.

LLOYD.

1

2

3

1. The Ocotillo, Fouquieria splendens, in leaf and flower, on Tumamoc Hill, April, 1906.

2. Young, rapidly growing shoot of Fouquieria splendens, bearing primary leaves. The developing spines are seen to be formed within the dorsal part of the petioles. On the right. near the

PLATE 2.