62 LIVING PLANTS 



shown it is not a protection against rain, be- 

 cause the plant soon becomes accustomed to 

 the falHng drops, and opens. The fact that 

 many plants of the temperate zone, among 

 which is the ordinary locust (Robinia pseud- 

 acacia), exhibit irritability to impact leads to 

 the suggestion that the plant must be very 

 delicately poised to be able to avoid the dan- 

 gers of changes in temperature, and that any 

 shock sets the protoplasmic machinery in 

 motion. 



The movements of mimosa in response to 

 the action of ether, chloroform and other an- 

 esthetics, as well as electricity, is due to the 

 direct action of these agents on the motor tis- 

 sues. A similar instance is afforded by the 

 action of changes in temperature upon ten- 

 drils. 



Equipped with an irritable organization of 

 such a high degree of complexity, mimosa can 

 easily hold its own in the swarm of competing 

 organisms in tropical climates. A similar or- 

 ganization would be highly disadvantageous 

 as well as impossible in high latitudes. 



