THE SENSES OF PLANTS. 



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THE SENSES OF PLANTS. 

 By Eev. Professor G. Henslow, M.A., V.M.H. 

 [Read October 22, 1912; Mr. E. A. Btjnyard in the Chadr.] 



Introduction. — All admit that there is only one and the same kind 

 of protoplasm or "physical basis of life" (Huxley), though it may 

 vary somewhat in its chemical composition, and the cell nucleus 

 behaves in a practically similar way in the production of cells 

 in all organic beings. In most animals, however, there is a more 

 or less well-developed protoplasmic nervous system, with distinct 

 organs of sight, hearing, smell, and taste; but one, the sense 

 of touch, is diffused over the whole body. In worms the sense 

 of sight is similarly diffused ; for earthworms come out of their 

 burrows in the dark, and they return as soon as light is felt in 

 the morning, but they cannot see it. Plants are similarly provided 

 with senses. Thus the different sensations of light and of darkness, 

 are diffused over every green or uncoloured surface; but the former 

 at least is localized in the chlorophyll granules. 



In some cases special organs are constructed which are keenly 

 sensitive to touch, as in many climbing and the so-called sensitive 

 plants. 



In insectivorous plants a sense of taste may be considered a 

 characteristic feature; since the glandular structures, which absorb 

 nutritious matter, refuse some things and utilize others, as will be 

 explained. 



In addition, something comparable to the sensation of thirst exists; 

 for the tips of roots will grow in the direction of moisture, often 

 overcoming difficulties in getting to it. Indeed, Darwin compared 

 the root-tip to a brain ! 



As to the senses of hearing and smelling, we have no evidence 

 that plants possess them, or that aerial vibrations are in any way 

 capable of producing any recognizable effects in plants. 



On the other hand, plants respond to the force of gravity, strains, 

 stresses, &c., by building up tissues expressly adapted to meet and 

 overcome them. 



The Sense of Sight. — Unhke the diffused sense of touch, that 

 of sight in animals is, of course, usually confined to special organs. 

 Our own sight is normally capable of distinguishing certain rays of 

 the sun, which appear coloured, as in the rainbow or solar spectrum, 

 which, when they are all oomhined, constitute white light. 



It is in this faculty wherein plants not only resemble us, but 

 utiHze the different rays for special physiological purposes respec- 

 tively. They cannot ''see" them, because they have no brains, but 

 their eyes " are the granules of green -coloured protoplasmic bodies, 

 called chlorophyll, within the cells. 



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