DARWIN MEMORIAL. 83 



kingdom — that all plants move and act. He has, so to speak, animated 

 the vegetable world. He has shown that whichever kingdom of 

 organic nature we contemplate, to live is to move. 



He blandly rebukes the vulgar notion that "plants are disting- 

 uished from animals by not having the power of movement," and 

 still more modestly says that "plants acquire and display this power 

 only when it is of some advantage to them." But is this the 

 whole ? Do animals display this power except when it is of some 

 advantage to them ? Certainly not. 



Darwin shows us that certain parts of all plants are at all times 

 in motion ; not merely the molecular activities of their tissues and 

 of the living protoplasm in their cells, but organized movement of 

 parts. Every leaf, every tendril, every rootlet, possesses the power 

 of spontaneous movement, and under nearly all circumstances actu- 

 ally exercises that power. 



There are a great many distinct kinds of movement, depending 

 in all cases upon the special advantages thereby gained to the^lant. 

 The laws under which these movements take place have received 

 from him an admirable terminology. Most of them are condi- 

 tioned either by light, by gravity, by radiation, or by insect agency. 



We thus have of the first class, heliotropism, or movement to- 

 wards the light ; apheliotropis?n, or movement from the light ; 

 diahcliotropism, or movement at right angles to the source of light ; 

 and paraheliotropism, embracing such movements as screen the 

 plant from excess of light. 



To the second class belong: geotropism, or movement towards 

 the earth or into the soil ; apogeoiropism, or movement contrary to 

 the force of gravity; and diagcotropism, or movement at right 

 angles to the force of gravity. 



The third class embraces the so-called nyctotropic movements of 

 plants by which they appear to sleep, and which prove to be devices 

 for the prevention of excessive radiation of the plants' heat. 



Under the fourth class fall all those wonderful movements which 

 aid the plant in preventing self-and securing cross-fertilization, a 



