PLANTS WHICH EXHIBIT MOVEMENTS IN THE CAPTUEE OF PREY. 147 



tenth, and so on, to a hundredth, and that the speed of transmission is susceptible of 

 measurement. The movements occasioned in protoplasts situated at a distance from 

 the seat of irritation by the stimulus propagated from its vicinity are, according to 

 the position of the stimulating object, sometimes in one direction, sometimes in 

 another, but in every case they are purposeful and for the benefit of the whole 

 organism. 



Investigations with a view to determining the degree of sensitiveness of 

 Drosera leaves yielded the following results. A particle of a woman's hair, 02 mm. 

 long and weighing 0000822 mg., when placed upon a gland of Drosera rotundifolia, 

 caused a movement of the tentacle belonoins; to the excited eland, which manifested 

 itself externally as an inflection. If so minute a body of the kind is placed on the 

 human tongue, its presence is not perceived, so that the sensitiveness of the 

 protoplasts in the glands of the sun-dew is greater than that of the nerve extremities 

 in the tip of the tongue, though the latter are well known to be the most sensitive 

 in the human body. A four-thousandth part of a milligram of ammonium 

 carbonate sufficed to induce motion, as also did ^ ^,^^ 1^ mg. of ammonium phos2:>hate, 

 It would lead us too far to consider all the experiments in detail, but they point to 

 the conclusion that liquid substances stimulate more strongly than solid bodies, and 

 that the more nutritious to the plant the material placed ujoon the gland, the more 

 ijuickly does the inflection of the tentacles ensue. 



The propagation or conduction of a stimulus from cell to cell, as it takes place 

 in the cell-community constituting a sun-dew leaf, may be compared to the 

 conduction of stimulus by nerves from a sense-oi-gan to the central organ, and of the 

 force of will from the brain to the muscles. This transmission is conceived to be a 

 progressive movement afiecting the ultimate particles of the nerves, and comparable 

 to the conduction of sound, light, and electricity; but no one has yet succeeded in 

 making these movements visible. So much the more interesting is it to be able to 

 see and follow in the glands and tentacles, by the aid of very slight magnifying 

 power or even with the naked eye, the material change which occurs in the 

 protoplasts of the sun-dew leaf when they are receiving or transmitting a stimulus. 

 The pedicel of a tentacle is penetrated by one or two vessels with fine spiral 

 sculpturing on the inner surface, and around these are parenchymatous cells. The 

 gland has in the middle a group of oblong cells sculptured internally with very 

 delicate spiral thickenings ("spiroids"), and the vessel or pair of vessels i-unnino- 

 down the middle of the tentacle (see fig. 26 ' ) merge into these sjjiroids. A 

 parenchyma composed of two or three layers surrounds the median group of 

 spiroids. In each parenchymatous cell the protoplast is discerned forming a thick 

 lining to the wall, and having a continuous streaming motion: whilst within 

 the vacuole is contained a homogeneous liquid of a purple colour. If the minutest 

 fragment of animal matter, such as flesh or albumen, be placed on these cells it acts 

 as a stimulant on the contents of the cell-cavities, and the impulse manifests itself 

 in a division of the hitherto homogeneous purple liquid into dark, roundish, club- 

 shaped and vermiform lumps, cloudy spheres, and an almost colourless liquid. 



