ix, c, 5 Gates: Pioneer Vegetation of Taal Volcano 393 
more diverse than that of the island. Around the shore are the 
customary swamp and strand associations, followed by parang 3 4 
shrubs, particularly Acacia farnesianaf and later by a number 
of trees. Near the shore, especially on the south and west, are 
large groves of bamboo. 
TAAL ISLAND 
In October, 1913, the volcano island, itself, was not devoid of 
vegetation, but vegetation was very restricted, occuring only 
near the shore and part way up some of the slopes. 
The physiography of the main body of the island is of unusual 
interest. As it is entirely covered with a deposit of loose ashes 
and mud and is unprotected by a covering of vegetation, the 
heavy tropical rains, which amount to from 1,750 to 2,000 mm 
per year, run off with great rapidity. The amount and diversity 
of erosion is enormous. The formation of sharp drainage sys- 
tems, the development of gorges, and the deposition of fans and 
deltas have proceeded to a remarkable degree. The steeper 
slopes of the ridges are scarred with small vertical fissures, 
which quickly concentrate the rain water in the valleys below. 
In rushing to the lake the rain water scours out deep canons. 
Of a number of these canons that were explored the follow- 
ing account, taken from a letter written by Doctor Gleason, is 
typical : ♦ 
Beginning as a narrow channel about a meter wide and deep, with flat 
bottom and vertical sides, it followed a sinuous course for over a kilometer 
to its mouth. As small lateral tributaries joined it, it increased in size 
until it became 50 meters wide with vertical turreted walls, 25 meters high. 
At intervals the depth is suddenly increased by abrupt drops of 1 to 4 
meters, and there the canon walls may approach each other until one’s 
shoulders touch both sides as he passes through. It is noteworthy that in 
such places the width of the canon is always greatest at the bottom, 
indicating a rapid growth of the stream system. At the mouth of such 
a system it broadens out into a huge fan, in some cases half a kilometer 
across, piled with boulders at its head, with smaller debris in the middle, 
while at the lake shore the deposits are of sand, fine gravel and pumice. 
There are scores of such embryonic river systems, large and 
small, on the island. The inner face of the crater is similarly 
eroded. 
Between the drainage channels, which are perfectly dry ex- 
3 A local Philippine term indicating thickets and second growth forests. 
4 The identifications of the seed plants were either made or verified by 
Mr. E. D. Merrill, botanist in the Bureau of Science, Manila, P. I.; those 
of the ferns by Dr. E. B. Copeland of the College of Agriculture, Los 
Banos, P. I. 
