846 



THE POPULAR SCIENCE MONTHLY. 



suits of special research in some by-path or 

 other subordinated to the main course of the 

 biological system associated with his name ; 

 and it has been an unfailing source of in- 

 terest to see the central ideas of the evolu- 

 tion and the continuity of life developed in 

 detail through a series of special treatises, 

 each wellnigh exhaustive of the materials 

 available for its subject. It is in the de- 

 partment of plant-life that he has of late 

 years devoted himself to working out the 

 laws which govern the whole realm of vital 

 phenomena. That these laws in their origin 

 and ultimate operation are common to plant 

 and animal alike has long formed a charac- 

 teristic principle or axiom of his philosophy. 

 In the experimental study needed for the 

 elaboration of the vital processes and the 

 making good the resulting generalizations, 

 the kingdom of plant-life offers decided 

 advantages beyond that of animals, if it 

 were only that observations of this class are 

 free from all possible taint of inhumanity. 

 Mr. Darwin has in the quietude of his hot- 

 house, and with a boundless variety of forms 

 for selection, experimented upon the vital 

 organism of plants, seconded by the untir- 

 ing energy and patience of his son. Night 

 and day seem to have come alike to the aid 

 of this enthusiastic pair of naturalists. The 

 electric light has served them on the failure 

 of the sun's beams, and has in truth opened 

 up of itself a wholly new field for observa- 

 tion as regards the agency of light upon the 

 phenomena of life. To the vista of knowl- 

 edge revealed by these experiments upon 

 the elementary processes of life in move- 

 ment, growth, nutrition, respiration, sensa- 

 tion, etc., imagination can set no bounds. 

 It is impossible, Mr. Darwin remarks at the 

 close of his record of these interesting ex- 

 periments, not to be struck with the resem- 

 blance between the foregoing movements of 

 plants and many of the actions performed 

 unconsciously by the lower animals. This 

 analogy has been made the subject of much 

 interesting investigation by Sachs, Frank, 

 and other leading biologists on the Conti- 

 nent, and we may expect that the highly 

 original and elaborate experiments record- 

 ed in the volume before us will give fresh 

 stimulus to this most important course of 

 investigation, laying as they do a new and 

 more solid basis for the comparative study 

 of plant and animal life. Plants, of course. 



possess neither nerves nor a central nervous 

 system, and there is consequently lacking in 

 them that which gives its most distinctive 

 character to animal life as a whole. Yet 

 that sensitive impressions are present in 

 plants, with the power of movement in obe- 

 dience to the stimulus thereby imparted to 

 the organism, may be held to be conclusively 

 shown by facts such as those produced by 

 Mr. Darwin. Most striking of all, he urges, 

 as a point of resemblance, is the localiza- 

 tion of their sensitiveness, and the trans- 

 mission of an influence from the excited 

 part to another, which consequently moves. 

 May it not be inferred that in animals the 

 nervous structures serve merely for the more 

 perfect transmission of impressions and for 

 the more complete intercommunication of 

 parts ? From the earliest sign of germina- 

 tion in plants namely, the protrusion of 

 the radicle from the seed-coats under the 

 soil there is manifest a sensitiveness to 

 external influences, with a movement in re- 

 sponse to the conditions of light or press- 

 ure, etc., which is not sharply to be dis- 

 tinguished from the rudimentary intelligence 

 in animals. In the sensitive point or tip 

 of the radicle, which we might compare 

 with the antennae in insects, there is to be 

 seen an organic power equivalent, in a lesser 

 degree, to the action of the brain in the 

 lower animals : 



We believe that there is no etructure in 

 plants more wonderful, as far as its functions 

 are concerned, than the tip of the radicle. If 

 the tip be lightly pressed or burned or cut, it 

 transmits an influence to the upper adjoininp; 

 part, causing it to bend away from the affected 

 side ; and, what is more surprising, the tip can 

 distinguish between a slightly harder and softer 

 object, by which it is simultaneously pressed on 

 opposite sides. If, however, the radicle is 

 pressed by a similar object a little above the 

 tip, the pressed part does not transmit any in- 

 fluence to the more distant parts, but bends 

 abruptly toward the object. If the tip perceives 

 the air to be moister on one side than on the 

 other, it likewise transmits an influence to the 

 upper adjoining part, which bends toward the 

 source of moisture. When the tip is excited by 

 light (though in the case of radicles this was as- 

 certained in only a single instance) the adjoin- 

 ing part bends from the light; but when excited 

 by gravitation the same part bends toward the 

 center of gravity. In almost every case wo can 

 clearly perceive the final purpose or advantage 

 of the several movements. Two, or perhaps 

 more, of the exciting causes often act simultane- 

 ously on the tip, and one conquers the other, no 

 doubt in accordance with its importance for the 



