placed. The stalk-cell is cylindrical. On the axis of C. microphyllus there are large cells, bearing clothing hairs intercalated amongst epidermal cells of ordinary dimensions.
The glandular hairs are placed in epidermal depressions and consist of an unicellular stalk-cell seated upon an epidermal cell which is much depressed and of a head. The head is either club-shaped and divided by horizontal walls as in. G. cretica (fig. 224) and G. glomeratus, or spherical and divided both by horizontal and vertical walls as in C. microphyllus (fig. 228), or flat and divided by horizontal walls as in T. sindica (fig. 231)
The lower cells of the head of club-shaped glands are also vertically divided (fig. 224). The walls of external glands with spherical heads are very thin. External glands seem to be absent in. B. latifolia.
Clothing hairs as well as external glands are less numerous on the axis than on the leaf. This is due to the expanded surface of the latter which is more exposed to direct rays of the sun.
Structure of the Axis. — The epidermis consists of tabular cells with outer and inner walls thickened and convexly arched outwards and inwards respectively. The lateral walls undulated in C. cretica and G. glomeratus. In G. microphyllus large pyramidal cells are inter- calated amongst epidermal cells of ordinary dimensions and usually bear clothing hairs. The cuticle is striated. The primary cortex is characterised by the presence of assiruilatory tissue formed either of palisade cells as in G. cretica (fig. 225) and C. microphyllus (fig. 229) or of chlorenchyma as in other members (fig. 234).
The pericycle in G. cretica and in both the species of Convolvulus is composed of closely placed long thin groups of stone-cells ; in I. sindica it forms a composite ring of stone-cells. In B. latifolia the pericycle consists partly of isolated stone-cells and partly of very small stone-cell groups. It undergoes reduction on a small portion of the lower side of the inclined axis of C. cretica, where it consists of a few isolated stone-cells. A well developed sclerenchymatous pericycle is necessary on the upper side of the inclined axis to prevent the axis from bending.
The wood is composite. The vessels have simple perforations and the medullary rays are uniseriate. The vessels are numerous and are arranged in rows in G. cretica (fig. 225), C. glomeratus and I. sindica (fig. 234) ; in other members the vessels are few. The abun- dance of interfascicular wood prosenchyma is inversely proportional to that of vessels.
In both the species of Convolvulus and in /. sindica small portions on diametrically opposite sides of the wood-ring are much narrowed 1239—10
