PLANTS WHICH EXHIBIT MOVEMENTS IN THE CAPTURE 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 0:000822 mg., when placed upon a gland of Drosera rotundifolia, 
caused a movement of the tentacle belonging to the excited gland, 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 553,55 mg. of ammonium phosphate, 
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 upon the gland, the more 
quickly 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-organ 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 affecting 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 
seulpturing 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 running 
down the middle of the tentacle (see fig. 26!) merge into these spiroids. 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. 
