116 MANGROVE SWAMPS 
In Table XXI are given the specific gravities of various man- 
grove-swamp woods as determined by Cox. From this table it 
will be seen that the woods of the Rhizophoraceae have a high 
specific gravity, averaging about 0.9. Usually the mature heart- 
wood of all Rhizophoraceae sinks in water. As all well-seasoned 
woods have very nearly the same calorific value per unit of 
weight, the specific gravity is highly important in determining 
the relative fuel value of different woods. The specific gravity 
also indicates certain other factors. In general it may said of 
woods otherwise equal, that those with low specific gravities 
kindle easily and flash quickly, the fire spreading rapidly; while 
those of high specific gravity behave in the opposite way. 
From the determinations of specific gravity, Cox has made 
comparisons of the fuel value of certain North American woods 
and of the mangrove-swamp species of the Philippines. Good 
woods include those having specific gravities between 0.60 and 
0.75. Among the North American species classed as good are 
hard pines, maple, ash, beech, birch, elm, black walnut, and a 
number of different oaks. The only mangrove-swamp wood 
placed by Cox in this class is tinductinducan (Aegiceras cornicu- 
latum). Very good woods are those with specific gravities be- 
tween 0.75 and 0.90. North American woods included in this 
class are some of the oaks and various species of hickory. In 
this class Cox includes tabigue (Xylocarpus moluccensis), pagat- 
pat (Sonneratia caseolaris), and langarai (Brugwiera parviflora) . 
Cox does not mention any of the North American species as 
having excellent woods, that is with a specific gravity greater 
than 0.9. In this class are included pototan (Bruguiera conju- 
gata), bacauan (Rhizophora mucronata), catutan (Bruguiera 
sp.), tangal (Ceriops spp.). This comparison emphasizes the 
very high value of the mangrove-swamp species for firewood. 
In Table XXII are given the analyses and calorific determina- 
tions made by Cox on air-dried bark. 
