68 A PRIMER OF BIOLOGY 



plant is certainly almost equally liable to injury, but 

 even though it recognised coming misfortune it could 

 not escape from it. As a corollary we may note 

 that the majority of non-motile animals, such as 

 sea-anemones, corals, zoophytes, barnacles and such 

 like, are aquatic and have their organic food brought 

 to them by water currents. Non-green plants, again, 

 though dependent on organic food materials, make 

 up for the want of locomotory power by the produc- 

 tion of enormous numbers of offspring, and distribute 

 them far and wide on the chance of some few reaching 

 an appropriate and favourable habitat. 



For the same reason the senses of smell, of hearing, 

 and of sight are well developed in animals, both for 

 the avoidance of injury and for the procuring of food 

 in the first instance, whilst such senses would be 

 useless to plants and are not developed. As for the 

 sense of taste the raw materials absorbed by plants, 

 such as carbon dioxide, water, and the salts of the 

 soil, are absorbed irrespective of whether they are 

 tasteless or otherwise, while the organic substances 

 used as food by the animal, have every possible 

 variety of flavour, and require to be discriminated 

 by the organism. 



The stimulation or excitation of these varied 

 sensory structures, be they differentiated and 

 undifferentiated, is often followed by movements 

 or indications of appreciation or otherwise, in regions, 

 it may be, far removed from the point of application 

 Transrois- of the stimulus. Thus, for example, a touch applied 

 suinufi. ^0 one of the segments of a Mimosa leaf is followed 

 by movement not only of that segment, but also of 

 all the segments in the vicinity. It follows from this 

 that the stimulus must have been transmitted from 

 the point of application to distant points. How is 



