770 
GENERAL CONDITIONS OF PLANT-LIFE. 
the chlorophyll-granules which are carried along by the very watery protoplasm accu- 
mulate at various spots. A current from thirty elements causes permanent cessation of 
the movement even if the connection is only momentary. Induced currents act like 
constant ones ; but the number of induction-shocks which pass through the cells in a 
unit of time appears to have no considerable influence on the action. 
The changes of form of protoplasm under the influence of a sufficiently strong elec- 
tric current are, according to the observations of Heidenhain, Brücke, Max Schultze, 
and Kühne, similar to those caused by a high- temperature near the extreme limit or 
beyond it. From those of Kühne it appears to result that protoplasm is a very bad 
conductor of electricity, and that the excitement caused by a current at particular 
spots in the protoplasm is not easily transferred to other spots. 
Cohn, Kabsch, and others, state that weak induction-currents act on the sensitive 
parts of the leaves of Mimosa, the stamens of Berberis, Mahonia, and Centaurea Scabiosa, 
and the gynostemium of Stylidium gram'mifolium like concussion or contact, the parts 
moving as if under the influence of these agencies. According to Kabsch, stronger 
induction-currents, which permeate the whole plant, destroy the sensitiveness of the 
gynostemium of Stylidium even for mechanical excitation ; but after half an hour the 
sensitiveness again returns. The statement of Kabsch is noteworthy that the move- 
ment of the leaflets of Desmodium gyrans are permanently prevented by stronger in- 
duction-currents, which however do not kill them. 
Sect. io. — Action of Gravitation on the Processes of Vegetation^ 
Since the attraction of the earth acts uninterruptedly on all parts of the plant, the 
entire vegetable organisation must be so contrived that the weight of the separate 
parts of the plant is serviceable, or at least not injurious, to the various purposes of 
the life of the plant. 
In observing these relationships the first thing is to distinguish between those 
contrivances which have for their object to bring the weight of the parts of the plant 
into harmony with the purposes of its life — gravitation itself not taking any direct 
recognisable part in the attainment of these objects — and those phenomena of 
vegetation on the other hand which are brought into existence by the direct influence 
of gravitation on the mechanism of growth. 
To the first of these groups belongs the fact that the branches and foliage of 
upright stems are distributed nearly equally on all sides, and that in larger plants 
the firmness and elasticity of the masses of tissue in the stem is promoted by the 
formation of wood, or is brought about by other means, as for instance in the trunk 
of Musa. But since it is very common in the organic world for the same purpose 
to be attained by very different means, slender dehcate stems with but Httle wood 
can protect themselves from sinking down and can expose their foHage to the light 
by twining round firm supports, or by climbing with the help of tendrils, hooks, 
spines, &c. The same purpose is evidently served by the various floating con- 
trivances of water-plants and those of fruits and seeds ; in all these cases the structure 
is obviously adapted to make the weight of the part of the plant serviceable or at 
least not injurious to its life ; although it cannot be maintained that gravitation takes 
any part in the formation of wood, in the sensitiveness of tendrils, or in the produc- 
tion of a floating apparatus. The only explanation of these arrangements lies in 
^ These statements are intended in the first place to draw the attention of students to the pro- 
cesses of vegetation which are especially influenced by gravitation. Its action on the mechanism of 
growth will be fully described in Chap. IV, where also the literature is quoted. 
