512 SCIENCE PROGRESS 



for the assimilation of its principal food, and although a few 

 animals possess chlorophyll the vast majority do not : con- 

 sequently chlorophyll, is a distinct feature of vegetal existence. 



Again, the plant is surrounded by an almost impervious 

 envelope of cellulose, and although a few animals are said to 

 possess this substance, the great majority are destitute of it : 

 therefore it constitutes a special vegetal characteristic. No 

 plant has visual organs, and though what are known as eye- 

 spots have been observed in plants, these probably serve as 

 means whereby greater response to light is obtained. It is 

 needless to say that no plant possesses the semblance of a 

 heart. 



Luminosity is a characteristic of plants as well as of 

 animals, but while in the former the effect is mainly produced 

 in swarms of minute organisms, in the latter it appears in 

 higher forms — in worms and fishes. 



Electrical conditions differ in intensity in the two kingdoms. 

 In plants, so far as our present knowledge goes, the currents 

 set up by metabolic changes or the movements of water are 

 very faint. No plant yet discovered exhibits the same 

 phenomenon as the electric fishes which are capable of impart- 

 ing shocks. Dioncea muscipula, which among the plants pro- 

 duces the strongest currents, is precisely one that partly feeds 

 on insects. In animals not only do appreciable currents occur, 

 but in man there are rare but well-authenticated cases where 

 the whole or part of the body gives rise to what appear to 

 be magnetic forces. 



It is hardly necessary to say that it is impossible to speak 

 of intelligence in plants in the same terms as of intelligence in 

 animals. All that corresponds to an animal intelligence in 

 plants is the well-known sensitiveness to light which causes 

 the plant to turn its leaves to the luminous source — undoubtedly 

 a chemical effect— and the "movement" of petiole and leaves 

 produced in certain plants of which Mimosa pudica is the best 

 example in response to stimulus. But this movement is not 

 conscious movement, and it is now known that it is caused by 

 a difference of turgidity in the protoplasm of the cells brought 

 about either under the influence of darkness or by shock. 



In the matter of longevity, the passivity of plant life appears 

 to be in its favour, since none of the higher animals have the 

 longevity of many trees. Few animals hibernate. The forces 



