THE REGION OF GREATEST STEM THICKNESS IN 
RAPHIDOPHORA 
Frank C. Gates 
To one accustomed to expect the greatest diameter in the oldest 
part of the stem, several tropical vines are interesting exceptions. 
Conspicuous in this respect are the araceous genera, Raphidophora 
and Epipremnum. Vines of Raphidophora merrilUi Engl., growing at 
Los Banos, Philippine Islands, were chosen for a series of measurements 
to present the anomaly more clearly. Measurement of the thickness 
of the stem was taken at 5 cm. intervals beginning at the tip. Of the 
37 plants employed the measurements of 7 are given in the accom- 
panying table. 
In each case it will be noted that the oldest part of the stem is 
not as thick as near the tip. In an extreme case the stem was more 
than seven times as thick near the tip as it was in the oldest region. 
In all cases the oldest region had the smallest diameter, which in the 
plants measured was 0.15 cm. The greatest thickness of any stem 
w^as 3.2 cm. At the tip, where the developing tissues have not yet 
reached their full size, the diameter of the stem is somewhat less 
than the maximum thickness, which however occurs within 15 cm. 
of the tip. 
Further analysis makes this condition seem less anomalous. As 
the plant becomes larger the new leaves are larger, carry on more 
photosynthesis and thus furnish more food. This food is carried only 
very short distances in the stem. Absorption by clingfast roots, 
which occur along the whole stem, adds materially to the water 
supplied through the main root. Owing to the large number of 
side roots, the main root performs proportionally less and less work, 
yet is of value as it is usually rooted in the ground, where there is a 
permanent water supply. The side roots obtain their water supply 
from the water soaked up by the debris accumulated between them 
and the tree trunk upon which the vine is growing. This is entirely 
ample during the rainy season. It frequently happens that side roots 
may grow out and down to the ground. This further reduces the 
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