CO-ORDINATION jg 



narrowing or dilatation of blood vessels, the beating of the heart, 

 to which the pressure of the blood is due, are all affected, and thus 

 the necessary co-ordination is brought about. 



DIFFERENCES BETWEEN ANIMALS AND PLANTS 



We have now to observe what are the differences between 

 animals and the members of the other principal division of living 

 beings, the plants. There is no fundamental difference in the 

 composition of the protoplasm which is the essential part of all 

 living things, nor do they differ in the essentials of their life. 

 This will be seen if we compare instances of the activities of plants 

 with those which in the foregoing paragraphs we have drawn 

 from the lives of animals. That the protoplasm of plants is irritable 

 we see in such cases as the turning of a sunflower towards the 

 sun, or the stimulation by gravity of the stem to grow upward 

 and root downward. That it is automatic appears in such facts 

 as the slow turning of the tendrils of climbing plants till they 

 meet with objects to which they can cling. That it has conductivity 

 can be seen when a stimulus given to the leaf of a mimosa causes 

 distant leaflets to fold. That it can execute movements may in 

 many cases be seen under the microscope, when it will be found 

 to stream round the cell. That it makes substances by chemical 

 activity and secretes them is illustrated by the long list of drugs 

 and other substances obtained from plants. That it grows and 

 reproduces need not be argued. In the sexual reproduction of 

 the higher (or flowering) plants, the part of the sperm is played 

 by bodies produced from the pollen, that of the ova by 'egg- 

 cells ' which are contained in the flowers, in organs known as 

 carpels. 



For all this agreement in essentials, however, there are 

 between most animals and most plants distinctions which are 

 both far-reaching and obvious. We may take our start from 

 familiar notions on the subject. Anyone who tried to state in 

 words the ideas which he had unconsciously formed of animals 

 and plants would probably find them to be somewhat as follows : 

 An animal is a being that moves and feeds ; a plant is a green 

 thing that grows in the earth. Let us examine these notions. 

 It will be best to base our analysis upon our definition of a plant. 

 We find that the information it implicitly contains is : (i) That 

 the plant is green, (2) that it does not swallow food, but draws 



