Mr Smith, Physiology of Plants in the Tropics. 297 
that there was the largest amount of young growth in February, 
the driest month of the year. The theory is suggested that only 
then is there sufficient transpiration to supply the necessary 
mineral food for rapid growth. The greater transpiration 
produced by the higher temperature of the young leaves owing 
to their red colour would assist in obtaining this mineral food 
supply. 
(y) Respiration of Hydrilla verticillata, a tropical water-weed. 
Values for the respiration from 7° — 50° 0. were obtained, 
in each case within two hours from the beginning of the 
experiment. These when plotted produce a curve which 
shows increase of respiration with temperature according to 
the Van t’ Hoff rule, the coefficient for an increase of 10° C. 
being 2‘2. The values go on increasing up to the death-point 
of the plant. 
von. xiv. pt. in. 
20 
