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ROBINSON. 
or without the Philippines altogether, often to the north. It now 
seems possible to divide the lower levels into two zones, roughly western 
Luzon and the rest of the Philippines. 
For fear of misunderstanding, it may be stated at the outset that 
there are very many species that are found in both these regions, some- 
times equally commonly in both, others more common in the one than 
in the other, and that these are not only weeds, and plants of the parang 
or jungle, but true forest species as well. It may further be postulated, 
that as the flora of the levels under discussion is undoubtedly Malayan, 
it is the northern extension which requires examination. 
Now, so far as the present state of our knowledge permits statement, 
it is certainly the. case that many species of the more southern islands of 
the Philippines extend up the east coast of Luzon, but not up the 
western; apparently a much smaller element extends up the western 
but not up the eastern; it has already been stated- that a third extends 
up both. 
Moreover, this division is at once geographic and ecologic, from the 
standpoint of the plants ecologic, but the ecology based on rainfall, and 
that in turn on the location of the principal mountain masses of Luzon. 
The west coast of Luzon has a prolonged dry season; on the east coast 
the rain is much more uniformly distributed, and the dry periods are 
of much shorter duration. 
Luzon has also a southern coast and the evidence available indicates 
that it is for this purpose to be classed with the eastern. Moreover 
the mountain ranges are not continuous. Consequently the plants of 
the eastern coast are often also found in Laguna, on the slopes of Mount 
Maquiling and Banajao. North of Banajao and Banajao de Lucban, 
the divide between the Lake and the Pacific is less elevated, and its 
western slope is more nearly opposite the eastern slope of these moun- 
tains. We would therefore expect, and we do find, that many plants 
found on these two mountains also occur on the western slope of the 
Pacific divide, and in many cases extend also to the hilly country in 
the northeast of Rizal or even farther to the north. A still farther 
western extension is to the hills in the east of Bulacan, which has here 
been included in the western slope of Luzon, causing several of the 
exceptions hereinafter noted, these more nominal than real. Polillo is 
politically a part of the Province of Tayabas, but when Tayabas is 
named in the lists of distribution, the reference is to the mainland only: 
similarly, Rizal refers only to the hill district in the northeast of that 
province. 
The further distribution of the more localized flowering plants of 
