30 The Philippine Journal of Science m4 
nearly entire extinction of the weeds and weed-like plants that 
cannot, unaided by man, compete with the indigenous vegetation. 
In the Philippines, and this is probably true of the entire 
Malayan and Polynesian regions, the average weed cannot grow 
in the forested areas, and is equally excluded from the grass- 
covered areas, especially the vast tracts of land that are covered 
with the lalang or cogon grass ( Imperata cylindrica) , and other 
coarse forms such as Saccharum spontaneum, Themeda, etc. 
Few weeds are found in thickets, and those that do occur in such 
places are soon exterminated as the thickets develop into forested 
areas. In a well developed and long established “cogonal,” as 
these grass-covered areas are called in the Philippines, prac- 
tically the only species found over immense areas is the grass, 
Imperata cylindrica. In some places certain other plants are 
found intermixed to a slight degree, but weeds proper, that is 
those plants that are more or less dependent for their continued 
existence on land cultivated or otherwise disturbed by man, are 
entirely lacking or appear only along trails leading through the 
“cogonales.” These weeds are for the most part pantropic in 
distribution, and are excluded by natural conditions from im- 
mense areas comprised under several types of vegetation, such 
as the primeval and second-growth forests, to a large degree the 
thickets, and the open grass-covered areas. They are dominant 
in fallow lands, in and about cultivated areas, along roads and 
trails, in deserted clearings that have recently been in cultiva- 
tion, in clearings recently made, and in waste places in the 
vicinity of towns and dwellings. A very few thrive along the 
gravel bars in the beds of streams, and still fewer are found 
widely scattered in the grass-covered areas. 
The vegetative condition of Guam, before the advent of man, 
was undoubtedly a continuous forest. The same is undoubtedly 
true of the Hawaiian Islands. In discussing this matter with 
Mr. J. F. Rock, botanist to the Board of Agriculture and Forestry 
at Honolulu, who is thoroughly conversant with the vegetation 
of the group and with the prevailing conditions in Hawaii, he 
expressed the opinion that the entire land area, except where 
the vegetation was temporarily destroyed by volcanic eruptions, 
and the peaks of the higher mountains, was, before the advent 
of man, quite covered with continuous forests. One great factor 
in the recent destruction of the forest vegetation in Hawaii has 
been domestic and wild cattle, goats, and horses. These, intro- 
duced by man, have destroyed the underbrush and seedlings in 
the forests, and above all have injured the trees by breaking 
