29 
“ Plants feel — they respond to stimulus. They may not be able to 
communicate their sensations as some animals do ; but many of the 
latter are not a whit more communicative on this point than a sea- 
weed. We, as members of the Animal Kingdom, feel the impact or 
contact of other substances. Light, heat, cold, electrical disturbances, 
chemical substances, all make us feel ; and if the sensation be of a 
disagreeable nature, we get away from the source of irritation as fast 
as we can ; but if the sensation be pleasant, we endeavour to repeat 
it. In the case of ])lants the great stimuli are light and heat. These 
exert a powerful influence on the protoplasm, as has been shown again 
and again. The protoplasm of plants and the ‘sarcode' of animals 
have precisely similar properties. The action of light in giving rise to 
motion both in plants and animals is well seen in the lower organisms, 
which, if green — that is, if containing chlorophyll — move towards the 
light ; but if they have no chlorophyll, light has no special influence in 
determining their movements. Hence the motion witnessed would 
seem to be depended on the decomposition of carbonic acid gas, and 
the elimination of oxygen, which takes place under such circum- 
stances as already explained. The protoplasm which lines the cells 
has contractile poAvers, and these contractile powers are, as we have 
seen, set in action by the stimuli of light or heat, and probably by 
electricity. 
“ There are other movements in plants evincing sensibility. Human 
beings are apt to blush on the occasion of sudden strong emotions, 
and this blushing is due to a sudden iargezceme of the minute vessels, 
induced by their momentary dilatation. Plants execute movements, 
due, like blushing, to varying amounts of turgescence. In most active 
vegetable cells currents of fluids may be observed. These currents 
are not entirely dependent on contraction of the protoplasm, but on 
the varying degrees of absorption manifested in it. If one portion 
suddenly exerts a great power of absorbing Avater, there is a corre- 
sponding flow to meet the demand, hence imbibition causes turgescence, 
and the turgescence gives rise to the formation of currents in individual 
cells. When a number of such cells are closely packed together, and 
are influenced in the same way, not only is there a flow in the cells 
individually, but there is a rush of fluid from cell to cell, and conse- 
quently a movement throughout the whole organ thus affected. In 
this way the opening and closing of flowers, as well as the folding and 
unfolding of leaves, may to some extent be accounted for. The curious 
movement of the sensitive plants are to be explained in a similar 
manner by the SAvelling of certain of their tissues, this turgescence 
being stimulated or set in action by certain stimuli, and checked by 
others. Climbing plants and some tendrils exhibit two different kinds 
of movements — the one a spontaneous revolving power manifested in 
young active shoots, in some plants in one direction, in others in the 
contrary. The object of these revolutions is to allow the stem to 
attach itself to some support round which it may twine. How they 
are affected is not understood ; they seem to be spontaneous, and 
not under the influence of external conditions. The movements of 
most tendrils, howev'er, are directly excited by contact. A slight touch 
causes them to move. In orchids (see the label! um of Pterostglis, 
Calea7ia, &c.), and in many flowering plants, displacements take place in 
the stamens {sqg Berhens)yhi the style (see column in Stglidium) j or in 
