THE GENERAL CHEMISTRY AND PHYSICS OF PLANT-LIFE. 281 



Mimosa we are concerued with curvatures of the leaf-joint 

 (motile organ), in the stamens of Cynarece with shortening of the 

 organs. In both cases there is a sudden reduction in turgor ; 

 the .primordial utricle suddenly becomes very permeable to 

 water, allowing the water to pass through its interstices and 

 finally also through the cell-wall into the intercellular spaces. 

 Later this water is taken up by the cells, thus placing them 

 again in a state of irritability. 



The following statements are according to the explanation 

 given by Sachs, and have special reference to the petiole of the 

 ilfz'mosrt-leaf. 



1. The motile organ is supplied with two tissue-cushions: 

 the loioer cushion is irritable, the upper cushion causes the 

 movements. 



2. There is a high tension in the succulent parenchyma of 

 the two cushions ; in this condition they are said to be balanced. 

 In the irritable state there is also tension, but the tension be- 

 tween upper cushion and vascular bundle is greater than the 

 tension between lower cushion and vascular bundle. 



3. The decrease in volume in the lower cushion is due to the 

 escape of water from its cells, externally noticeable by a darker 

 coloration. The water escapes in part into the intercellular 

 spaces of the upper cushion, in jjart into the tissue of the stem 

 and a small portion into the vascular bundle. 



Behavior of Tendrils. Conduction of Stimuli. The Function of 

 Irritable Movements. 



In tendrils there is an irritable movement induced by con- 

 tact (not by shock) associated M'ith processes of growth. This 

 irritability is usually not general, but limited to one side of the 

 organ. Groivth is alivays reduced in the side irritated. As a result, 

 the tendril lying in contact with some sujjport, curves toward 

 that support by a process of circumnutation ; this brings other 

 portions of the tendril in contact with the support, the stimulus 

 is transmitted along the line of contact, finally causing the entire 

 free portion of the tendril to Aviud about the supjDort in the form 

 of a spiral; The stimulus is also continued toward the basal 

 portion of the tendril (continued from the point of contact above), 

 which cannot come in contact with the supjDort. The stimulus 



