HOW PLAM'.S L'SK ANIMALS. 27 



inflection varies from one to four or live hours, according to the 

 age and vigour of the leaf, the nature and size of the object, and 

 the temperature of the atmosphere. The inflection takes place 

 equally by day and night. An insect, as a fly with thin integu- 

 ments, causes a longer inflection than an insect, like a beetle, 

 with a thick covering. Strongly inciting substances, as drops of 

 milk, produce also an incurvation of the leaf, so that it resembles 

 a shallow cup. When tentacles, remote from an object caught 

 on the centre of the leaf, have become considerably deflected 

 towards it, they pour out an increased amount of secretion, 

 which soon changes its nature and becomes acid. Like the 

 gastric juice of the higher animals, the seci'etion possesses an 

 antiseptic power. If a small piece of meat be placed on the 

 tentacles, and anotlier be enclosed in the moss beside it, the for- 

 mer will remain fresh and untainted long after the latter has be- 

 come putrid and flUed with infusoria. When the juices of the 

 insect, or other object covered by the secretion, have been di- 

 gested and absorbed, the tentacles gradually unbend and assume 

 their natural position, awaiting the arrival of new and heedless 

 visitors. 



The extreme sensitiver.e.^s of the tentacles is worthy of 

 notice. '"It is an extraordinary fact," says Darwin, "that a little 

 bit of soft thread, one-flftieth of an inch in length, and weighing 

 tjne eight thousand one hundred and ninety seventh of a grain, 

 or of a human hair, eight one-thousandth of an inch in length 

 and weighing only one seventy-eight thousand seven hun- 

 dred and fortieili of a grain (.000822 milligramme), or particles 

 of precipitated chalk, after resting for a short time on a gland, 

 should induce some change in its cells, exciting them to trans- 

 mit a motor impulse throughout the whole length of the pedicel, 

 consisting of about twenty cells, to near its base, causing this 

 part to bend and the tentacle to sweep through an angle of 

 above 180 degrees."' He proved by experiment that far less 

 than the millionth of a grain of phosphate ofamnK)nia in solu- 

 tion, when al)Sorbed by a gland, acts on it and induces move- 

 ment. 



