PHILIPPINE WOODS. 
355 
( Dillenia spp.)| etc., and, in others, so small as to be invisible without 
the aid of a magnifying glass, as in acle ( Pithecolobium acle (Blco.) 
Vid.), betis (Illipe betis (Blco.) Merr.), camagon ( Diospyros spp.), or 
banaba ( Lagerstroemia speciosa (L.) Pers.). The pith-rays may be all 
of the same size in the same tree, or there may be some large ones (the 
primary pith-rays) running from pith to bark, and some finer (secondary 
rays) starting beyond the pith. Compound pith-rays, where several are 
crowded together, may also occur. Pith-rays may take either a crooked 
or a straight course from the pith to the bark, but if curved, they usually 
are not abruptly so. Tire height of pith-rays is variable ; they may be so 
short as scarcely to appear to have this dimension, or again it may be 
quite appreciable. 
Growth rings. — The wood is formed in layers about the pith; and 
these may be formed only during certain seasons, the tree resting the 
remainder of the time. Where this is the case, each period of growth 
produces a ring about the pith. These rings are found in nearly all 
woods of temperate regions and in some of those of the Tropics. Where 
but one of them is formed during the year, it is called an annual ring, 
hut manifestly, this name is not suitable for use with our woods, since 
we do not know whether one year sees the growth of one or of several. 
Consequently, the term annular, or seasonal growth rings has seemed 
preferable and will be used in this paper. 
Seasonal rings seem to be characteristic of some of our woods only. 
It seems probable that the same species may have them when grown under 
one set of conditions and not under different ones. It also appears that 
many trees exhibit rings of seasonal growth when they are young but 
not afterwards. We have begun, in cooperation with the Bureau of 
Forestry, a series of observations on the manner and rate of formation of 
growth rings, but it will necessarily be some years before any safe general 
conclusions can be reached. 
Distinct seasonal rings seem to be of constant occurrence in narra 
( Ptcrocarpus spp.), banaba (Lagerstroemia speciosa (L.) Pers.), calan- 
tas ( Toona spp.), ipil ( Intsia spp.), supa ( Sindora supa Mer.r.), molave 
(Vitex spp.), and several other woods, but there seems to be a consider- 
ably greater number where they are not so. 
False seasonal lings. — A number of woods show distinct, concentric 
lines bearing a 'strong, superficial resemblance to seasonal rings. These 
false rings may be caused by lines, of soft tissue, as is the case in dita 
( Alstonia scholaris E. Br.) and palo maria ( Calophyllum spp.), where 
they are so close together as to make it unlikely that they will often be 
mistaken. Lines of whitish resin-canals often give the appearance of 
seasonal rings in lauan ( Shorea spp.), apitong ( Dipterocarpus spp.), 
yacal (Hopea spp.), guijo (Shorea guiso Bl.), etc. These may readily 
be distinguished from the true seasonal rings by their irregularity of 
occurrence and by the fact that they usually fade out before completely 
