The wood is composite in all members. In species of Trian- thema it is composed of numerous xylem bundles which are embedded in interfascicular wood prosenchyma in more or less distinct concentric rings (figs. 140, 143). In species of Mollugo it is composed of large xylem bundles with vessels large and numerous and with little interfascicular wood prosenchyma (figs. 149, 153, 155). Vessels, in 0. decumbens, G. phamaceoides and L. indicum, are large and numerous and are uniformly distributed in the interfascicular wood prosenchyma. Thus the structure of the wood can be classified into three types — M, nudicaulis and M. Cerviana representing one type species of Trianthema another and 0. decumbens, M. hirta, G. phama- ceoides and L. indicum the third type.
The structure of the wood has undergone modifications
- (1) either due to the decumbent habit as in 0. decumbens in
which the wood cylinder is very much narrowed and the vessels are few and small on the lower side of the axis.
- (2) or to the direction of the prevailing wind as in T. triquetra,
G. phamaceoides and L. indicum, in which larger xylem bundles with vessels larger and more numerous occur on two opposite sides of the axis which represent the plane of the direction of the prevailing wind, while in a plane at right angles to this occur much smaller xylem bundle with vessels much smaller and less numerous.
These modifications are the result of greater functional activity on those sides which are more affected by wind in the case of erect axes, or by the sun and wind together in case of prostrate axes.
The pith consists of thick-walled calls in T. pentandra, M. hirta and L. indicum; in other members it is formed of thin-walled cells.
Oxalate of lime is found in the form of clustered crystals in the cortex and pith of T. triquetra, T. pentandra, 0. decumbens and M, hirta ; in L. indicum clustered crystals occur only in the cortex. Acicular crystals are found in the cortex and pith of G. phamaceoides.
Anomolous structures are represented by groups of soft bast embedded in the wood cylinder in T. triquetra.
General Review. — 'Epidermis consists of polygonal cells with outer walls usually thickened. Large bladder-like cells with water- storing function are intercalated amongst epidermal cells (figs. 141, 143). Stomata are depressed and are accompanied by ordinary epidermal cells. The mesophyll in T. triquetra (fig. 139) is character- ised by an extensive aqueous tissue. Oxalate of lime is found in the form of clustered crystals in the leaf and axis of most of the members. Styloids occur in M. nudicaulis and M. Cerviana; acicular crystals are present in G. phamaceoides. Hairy covering is present only an M. hirta
