385 
of grasses. Often reaching to a height of 15 or 20 meters, the bamboo 
is able successfully to compete with the dicotyledinous trees of the same 
height. ‘This advantage is best utilized during the favorable season, when 
conditions for growth and photosynthesis are at their maximum. While 
none of the bamboos of the Lamao Reserve are completely deciduous 
during the dry season, yet the total area of the foliage is much less then” 
than during the wet one. This is brought about in two ways. Mani of 
the leaves of individual shoots are shed, leaving them with from one-third 
to one-half as many leaves as they would have during the rainy season. 
In this way the bamboos simulate the semi-deciduous trees with which 
they grow. Those which remain may reduce their transpiration surface 
by curling up like grass. Again, some of the culms die down altogether 
during the dry season, thus reducing the transpiration surface of the 
clumps from which they spring. Grasses may either form sod by sending 
out runners or underground shoots which radiate in all directions from 
a common center, or they may be caspitose, when they are commonly 
known as “bunch” grass. Bamboos, like other grasses, may be repre- 
sented by species of both types, although the “bunch” type is the pre- 
dominant one on the Lamao Reserve. While the individual shoots are 
short-lived, the permanency of the “bunch” is maintained. To sum up, 
the half-grass and half-tree like habit of the bamboo is peculiarly 
fitted to a formation which is midway between the best expression of 
Schimper’s tropical rainy and his tropical savannah forest. 
Parkia roxburghit, the tree after which the dicotyledinous portion of 
the formation is named, is only one of a number which igs deciduous a 
part of the dry season. (PI. III.) While not so abundant as some of 
the other species of the same type, yet it is the largest and most con- 
spicuous one present. 
Within the Bambusa-Parkia formation there are many places where 
the bamboo element is altogether absent. This is more true of Parkia 
roxburghi, although the Parkia type (deciduous) is nearly always rep- 
resented by some species. Careful measurements of the chresard will 
no doubt show constant variations in different portions of the formation 
although, except for a narrow margin along the banks of the rivers, these 
differences are not thought to be great enough to justify a subdivision 
of this formation into two or more coérdinate ones. Rather, they are 
- all considered to be stages, physiographic or artificial, in the life history 
of the vegetation which the region is able to support and which is a 
mixture of the bamboo and of the semi-deciduous types expressed by the 
names of the formation. 
The map shows the general limits of the formation. Briefiy, it ex- 
tends from the upper limits of the littoral vegetation to a varying height 
on the side of the mountain. Making a liberal allowance for a tension 
line (ecotone) between this and the adjoining formation, it reaches an 
altitude of 75 meters on the south side of the reserve, while it runs up 
