480 Ewart . — The Effects of Tropical Insolation . 
perceptive organs. In Mimosa pudica the irritability is very 
marked and well differentiated, the main pulvini responding 
to the direction of the light in a diaheliotropic manner, the 
pulvini of the leaflets responding to the intensity only of the 
illumination, being paraheliotropic in intense light, diahelio- 
tropic in diffuse daylight, and nyctitropic in very weak light 
or darkness. It is mainly to the photochemical rays, which 
are most active in inducing the decomposition of chlorophyll, 
and in inducing light-rigor, that the pulyinus of the leaflet 
responds. 
The red pigment acts mainly and primarily as a protective 
shield against the more refrangible rays (green and blue). 
It has also a feeble heat-absorbing power, which may, in 
a few cases, possibly be of considerable or even primary 
importance. 
