VITAL FORCE, IXSTIXCT, AND SENSATION. 



53 



in search ol' tlie liest place to settle in, and in every pollen-tube as it grows 

 down through the entrance to an ovary and applies itself to one definite spot of 

 an ovule, never failing in its object. The water-crowfoot, in deep water, fashions 

 its leaves with finely divided tips, large air- passages, and no stoniata; whilst, 

 growing aliuve the surface of the water, its leaves have broad lobes, contracted 

 intercellular spaces and numerous stomata. Linaria Cymbalaria (see fig. 11) 

 raises its Hower-stalks from the stone wall over which it ci'eeps towards the light, 

 but as soon as fertilization has taken place, these same stalks, in that very place 

 and amidst unchanged external conditions, curve in the opposite direction, so as 



ris^. W.—Lhiatia Qymbalaiia drupijinjj its Seeds into Clefts in tlie Rocks. 



to deposit their seeds in a dark crevice The flower-stalk of Vallisneria twists 

 itself tightly into a screw and draws the flowers, which previously it had borne 

 upon the surface of the water, down to the bottom when their stigmas have been 

 covered with pollen-dust at the surface. These are all cases of unconscious action 

 for a definite object, that is to say, they are the result of instinct. 



If, however, we attribute instinct to living plants, it is but a step further to 

 consider them as endowed with sensation also. Feeling in animals is the con- 

 comitant of a condition of diiBturbance in nerves and brain caused by a stimulus, 

 which acts on the organs of sense, and is conveyed by nerves to the central 

 organ. The transmission of the stimulus and the excited state of the brain and 

 nerves are only molecular movements of the nervous substance, or, let us say, of 

 the protoplasm, for nerve-fibres and nerve-cells are simply protoplasm developed 

 in a particular manner. But the state induced by the stimulation of protoplasm, 

 which is what we call sensation, cannot be essentially diflerent in vegetable 

 protoplasm from what it is in animal protoplasm, since the protoplasm itself, 

 the physical basis of life in both plant and animal, is not different. In isolated 

 plant-cells, indeed, it may amount to such a concentration of the condition of 

 stimulation as to be called sensation, for the cell-nucleus is to all appearance 



