390 VEGETABLE PHYSIOLOGY 
green in consequence of the replacement of the air there 
by water. If a leaf is cut off just above the pulvinus and 
the plant allowed to recover from the effects of the injury, 
subsequent stimulation of an adjacent leaf causes water to 
exude from the cut surface of the pulvinus. The cases 
of the irritable stamens and stigmas are probably to be 
explained similarly. The closing of the leaf of Dionea 
(fig. 159) is due algo to a redistribution of the water in 
Fic. 159.—Luar or Dionea muscipula. 
1, open; 2, closed; 8, one of the sensitive spines (x 50); 4, glands on 
the surface of the leaf (x 100). 
the cells of a band of tissue lying along the mid-rib, 
brought about by a rapid change in the protoplasm, 
perhaps akin to contraction. In Drosera the inflexion 
of the tentacles has been found to be preceded by a 
peculiar churning movement of the protoplasm in the cells 
upon the side which becomes concave. This movement, 
which Darwin, who discovered it, called aggregation, is 
attended by a loss of turgidity. 
Morsturs.—Sensitiveness to variations in the moisture 
