482 The Physiology of Plants BOOK in 



differs from that of the combination of the absorption of 

 digested material with such tactile impulses, so that the 

 active mechanism of the leaf is not called into full play 

 unless useful results are secured. He described the changes 

 in the interior of the cells of the tentacles which are the 

 accompaniment and sign of stimulation, the mysterious 

 churning of protoplasm and sap to which he gave the name 

 aggregation. 



One of the most remarkable hypotheses which may be 

 found in his work is the view that the heads of the tentacles 

 exercise a definite influence upon the process of the 

 conduction of impulses, being not only seats of sensation, 

 but in a somewhat rudimentary fashion co-ordinators of 

 the transmission in such a way as to suggest a kind of 

 reflex action. Another very interesting discovery was that 

 like certain tendrils, the tentacles can discriminate between 

 contact with a solid body and the shock received by the 

 impact of drops of rain, failing to curve under the stimulus 

 of the latter. The researches of Pfeffer made ten years 

 later upon this point in connexion with the behaviour of 

 tendrils have already been alluded to. He showed that 

 both phenomena admit of the same explanation. 



In 1877 Batalin claimed that the movement effected by 

 the tentacle is a growth curvature. Correns supported him 

 in 1892 ; he killed a stimulated and curving tentacle by 

 immersion in boiling water and found that its curvature 

 remained permanent. 



In 1882 Schimper published the result of some researches 

 on the condition of the cells of the tentacles during and 

 after stimulation. He showed that after strong excitation 

 a precipitate falls in the cell sap, due to the formation of 

 some chemical secretion by the protoplasm. This was 

 observed also by Goebel in 1893, and was by him termed 

 granulation. Schimper distinguished between this pre- 

 cipitation and the churning movement of aggregation, 



