A WOODY STEM IN MERREMIA GEMELLA INDUCED BY 
HIGH WARM WATER 
Frank C. Gates 
In the large swamp a little west of Los Baiios, Laguna, Philippine 
Islands, Merremia gemella (Burm.) Hallier f. (Convolvulaceae) is a 
common vine which sometimes grows over Phragmites vulgaris (Lam.) 
Trin. and Sesbania (nearest 5. seshan (L.) Merr.). As both of these 
species grow in water the greater part of the year and Merremia is 
neither a parasite, like Cuscuta, nor an epiphyte, its roots must also 
be under water. This is not a normal condition for Merremia but it 
does adapt itself and lives. Consequently, even near the center of 
the swamp, one finds festoons of Merremia draped over the Phragmites 
and Sesbania, even when they are growing in water a meter deep. 
Usually the stem of Merremia gemella in dryland thickets and as a 
weed in cultivated land is herbaceous and dies down each year. Under 
the conditions obtaining in the swamp, the first and perhaps most 
striking thing seen is the prominent w^oody stem which may be as 
much as 20 mm. in diameter. 
As a seedling Merremia must start in the ground and is continually 
dependent upon the ground for certain mineral salts. The seedling 
develops into a vine, rapidly making its way to the upper story of 
vegetation and spreading out over whatever happens to be there. 
To do this the normal herbaceous stem appears to be sufficient under 
ordinary conditions. Most of the swamp area is submerged during 
the rainy season, so that the roots of Merremia are under water. In 
ordinary years they are not generally far under water — less than 25 
cm. rather than more. The sources of the water in the region are 
bubbling hot springs, whose temperature is usually between 70 and 
90° C. The water soon becomes cooled to a temperature between 30 
and 40° C, which several plants withstand. 
The high water of 1914 was very high, — more than 1.5 meters 
over considerable area. The water covered the hot springs, which 
however continued to heat up the water in their vicinity. In the 
immediate vicinity of the hot springs the plants were killed outright 
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