1883-84] Edinburgh Naturalists' Field Club. 153 



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

 man (Whately, 1780), that the tentacles were 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, which become 

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

 then those further ofl", 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 reinain in their original erect position. 

 Should the object be placed on the glands away 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, while 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 

 towards the centre. 



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

 bend. Darwin found that a bit of blotting-paper weighing -^\^ of a 

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

 slowly inwards. A bit of cotton-thread -jV of an inch in length, and 

 weighing -g-yVT of ^ grain, was next placed on a tentacle, and was 

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

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

 weighing ^s^.txt of ^ grfiiii> the other xi5"o of an inch in length, 

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

 of the same leaf, and these two tentacles were inflected half-way 

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

 round the same leaf remaining motionless. The smallest particle 

 which was tried, and which caused the tentacle to bend, Avas only 

 i-(j%^ of an inch in length, and weighed Tg.TTir 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 Avater 

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

 although repeatedly added, produced no efl'ect. Neither did the 

 disturbance of the secretion produce any eftect ; for long threads 

 were draAvn out by a needle and affixed to some adjoinmg object, 

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

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



