A WOODY STEM IN MERREMIA GEMELLA 
87 
and deleterious effects spread considerably further. Six weeks later, 
at the end of October, the temperature of the water a kilometer away 
from the hot springs was 27° C, whereas the surface water over them 
was 37 to 42° C. 
All of the Merremia in the vicinity of the hot springs was killed. 
Further away where the temperature did not go much above 30° C. 
the effect was to stimulate the growth of a woody stem. The secondary 
thickening was very irregular, forming what is known as anomalous 
structure. Beneath the warm water level, there was only a very little 
secondary thickening present, of the same general type as that above 
Fig. I. The edge of the creek in the center of a swamp, showing Merremia 
gemella cHmbing on Seshania. Seshania in fruit is nearly leafless. Los Bahos, P. I. 
October 31, 1914. 
the water but much poorer in amount and diversity of anomalous 
structure. The xylem vessels were noticeably larger in the part of 
the stem above the water. The bark above the water was rugged, 
but beneath the water it was quite smooth and compact. It was 
frequently covered with putrifying bacteria, but did not produce 
aerenchyma. When the stem was submerged during only the highest 
part of the high water and especially when it was twining around a stem 
of Sesbania, at the places where aerenchyma was produced by the 
Sesbania, short (less than 25 mm.), horizontal, clinging roots were 
developed from the stem of the Merremia. Entirely above the water 
