1883-84] EdinburgJi. Naturalists' Field Club. 153 



persons, the one a German (Eotli, 1779) and the other an English- 

 man (Whately, 1780), that the tentacles Avere sensitive, and that 

 insects were imprisoned by the leaves. These observations were 

 confirmed by another German observer (Nitschke) in 1860; by an. 

 American lady (Mrs Treat) in 1871 ; and the subject has been care- 

 fully worked out in this country by Mr Darwin and others. If a 

 small object be placed on the short tentacles in the centre of the leaf, 

 a motor impulse is conveyed to the surrounding ones, Avhich become 

 inflected over it, those nearest the centre becoming first bent, and 

 then those further off, until the whole of them are closely in- 

 flected over the object. The tentacles in the centre of the leaf do 

 not bend in this case, but remain in their original erect position. 

 Should the object be placed on the glands aAvay from the centre of 

 the leaf, however, the short tentacles of the centre become bent 

 towards the point of excitement, through a motor impulse being 

 conveyed to them from the excited glands. When a very minute 

 particle of meat is placed on one of the long exterior tentacles, it 

 bends towards the centre of the leaf, Avhile those surrounding: it 

 retain their original position. If the object be not too minute, and 

 especially if it contains soluble nitrogenous material, immediately it 

 comes in contact with the glands of the central tentacles a motor 

 impulse is transmitted to the surrounding tentacles, which all' bend 

 toAvards the centre. 



It is astonishing how minute an object Avill cause the tentacles to 

 bend. DarAvin found that a bit of blotting-paper Aveighing j^-g- of a 

 grain, placed in contact Avith three glands, caused them to curve 

 slowly iuAvards. A bit of cotton-thread -gV of an inch in length, and 

 Aveighing siVt of a grain, Avas next placed on a tentacle, and Avas 

 carried to the centre in 1 h. 40 m. Tavo particles of the thinner 

 end of a human hair, one being -^^-^ of an inch in length, and 

 Aveighing s-g-.Trr of a grain, the other y^^o of an inch in length, 

 and Aveighing a little more, Avere placed on glands on opposite sides 

 of the same leaf, and these tAvo tentacles Avere inflected half-way 

 toAvards the centre of the leaf in 1 h. 10 m., all the other tentacles 

 round the same leaf remaining motionless. The smallest particle 

 which AA'as tried, and Avhich caused the tentacle to bend, Avas only 

 ytkto of an inch in length, and Aveighed ts.tto of a grain. 



DarAvin's surprise Avas greatly excited not only by the minuteness 

 of the objects Avhich caused inflection, but as to how they could 

 possibly act on the glands ; for he found that small drops of AA^ater 

 many times heavier than the particles which Avere placed on them, 

 although repeatedly added, produced no eflect. I^either did the 

 disturbance of the secretion produce azay effect ; for long threads 

 were drawn out by a needle and affixed to some adjoining object, 

 and thus left for hours, but the tentacles remained motionless. If 

 repeatedly touched or brushed, however, although no object Avas left 



