Pandanus, Hibiscus tiliaceus, Erythina indica and Terminalia catappa 
are common. Less frequent are Pongamia glabra, Thespesia populnea, 
and Herttiera littoralis. Shrubs such as Cerbera odollam, Morinda 
citrifolia, and Clerodendron inerme occupy the edge or the more open 
places of the beach jungle. The scandent shrub Qutsqualis indica and 
the semi-herbaceous vine Wedelia biflora are nearly always present. Near 
small villages, where the beach has been cleared, the introduced thorny 
Prosopis julifora has succeeded in gaining a foothold and in some 
places it is the only woody species present. Occurring with it, but less 
abundant, are Pithecolobium dulce and Acacia farnesiana, both exotics. 
Calophyllum inophyllum which, in some places, appears on the open 
sandy beaches is, for the Reserve, confined to a more protected shore line. 
The only specimen of the valuable timber tree Intsia bijuga (ipil) 
which has been observed on the Reserve, was noted in this situation. 
In clearings in the Barringtonia-Pandanus formation are Ipomoea 
pescaprae, Canavalia obtusifolia, Spinifex squarrosus, and the weeds, 
Vernonia chinensis, Crotalaria retusa, Scoparia dulcis, Aerua lanata, 
Portulaca oleracea, Gynandropsis pentaphylla, and Datura fastuosa. 
More extensive observations of the vegetation of this formation outside 
the Reserve show that many plants enumerated by Schimper and others 
for the Indo-Malay region are also found in the Philippines, although 
a large number are not present in the limited area under consideration. 
(See map.) 
Genetic relations.—As the beach grows, the plants of the Barringtonia- 
Pandanus formation advance into the Pes-capre zone and eventually 
replace its vegetation, although the latter may still exist in artificial open- 
ings of the former. In the same way, the vegetation of the formation 
lying behind the beach in time occupies the older portions of the latter ; 
thus, on the Reserve, the plants of the Bambusa-Parkia are present therein, 
although here the artificial conditions render this relationship confusing. 
Indeed, only the frontal zone of the beach shows a pure expression of 
the Barringtonia-Pandanus formation. As soon. as this is penetrated, the 
character of the vegetation changes and relics of the former vegetative 
condition are then shown only by seattered individuals of Pandanus and 
the other species. 
The beach habitat and the ecological characteristics of the vegetation 
thereon.—The beach is essentially a xerophytic habitat. This is shown 
by the stunted condition of trees, the umbrella habit of Barringtonia 
speciosa and Terminalia catappa, the fleshy leaves of the Ipomoea, Cana- 
valia and others, and the hard, xerophytic leaves of all the tree species. 
The factors of the beach habitat which bring about the xerophytic 
condition of the plants growing thereon are not definitely known. Prob- 
ably a number of these are operative. Until lately it has been assumed 
that the plants of the strand and dunes are all halophytes. Investiga- 
