1923.} Ecology of Riverine Tract of Burma. 97 
widely separated and the forest becomes almost a savannah. 
The Indaing covers huge areas of Trrawadian sands as far 
north as 20°5’, provided the drainage is sufficiently good. 
Whilst the forest flourishes on a ferruginous sand its growth is 
prevented by a hard surface laver of laterite or “« iron- pan.” 
SAVANNAH FORESTS. 
3. Diospyros Forest. Diospyros birmanica hylion. With 
decreasing rainfall the Indaing grades into a type of forest 
which consists of roughly equal proportions of Diospyros 
hirmanica Kurz (Te), Termimalia tomentosa W. et A., and 
Pentaeme suavis A. DC. Still further north the last mention- 
ed becomes scarce and its place is taken by such trees as 
Tectona hamiltonii Wall. (Dahat), Dalbergia paniculata Roxb. 
(Tapauk) and Acacia catechu Willd. (Sha). The undergrowth 
is again almost entirely grass—Andropogum contortus Linn., 
A. apicus Trin. and A. serratus Thunb.—which tend to grow 
gregariously. This type of forest occurs mainly on the Irra- 
wadian, spreading also on to the sandier beds of the Pegu 
system. Poorly drained plateau portions are covered with 
a stunted forest or even a scrub especially of Dalbergia pani- 
culata, Pterospermum semisagittatum Ham., or Acacia catechu 
Willd. 

4. Vitex-Heterophragma Forest. Vitex-Heterophragma 
hylion. It is difficult to find a name for the very mixe 
forest which clothes the steep-sided ranges of hills of Pegu 
sandstones. The spurs of the hills are often covered largely 
by bamboo (Dendrocalamus strictus) whilst the trees in the 
chaungs and gorges grow tall and straight to considerable 
1eights. Among the more characteristic trees may be noted 
Vitex cf. limonifolia, Heterophragma adenophyllum Seem. {Pet- 
than), Stereulia colorata Roxb. var fulgens, Dolichandrone 
stipulata Benth. (Mahlwa), Odina wodier Roxb. (Nabe), : 
bax insigne Wall. (Didu, conspicuous though not numerically 
abundant) and Acacia leucophloea Willd. var microcephala 
Graham. The grassy undergrowth is more varied and often 
luxuriant, but Andropegum apicus Trin. is the most abundant 
Species. 
tona hamiltonii-Terminalia oliveri Forest (Dal 
ina 
5. Tec hi ‘eat 
Than Forest). Tectona b.—Terminalia o. hylion. This ' 
oliver, Brandis (Than) produces straggling csi ch of 
The grassy undergrowth consists mainly of a poor growth o 
