290 VEGETABLE PHYSIOLOGY 



power of active movement or locomotion. Zoospores of 

 many of the Algae and Fungi, and the antherozoids of most 

 of the Cryptogams effect this locomotion by means of cilia 

 which wave to and fro vigorously in the water in which 

 they find themselves. The proportionate amount of 

 energy which they expend in this way is very great com- 

 pared with the total amount which they possess. Other 

 movements which are not dependent upon ciliary action 

 are not uncommon. The amoeboid movements of the 

 Myxomycetes or slime fungi, the rotation and circulation 

 of the sap in many cells, the other internal movements of 

 protoplasm, the hitherto unexplained movements of diatoms 

 and the oscillations of certain filamentous Algae, illustrate 

 these. All alike are dependent upon a certain expenditure 

 of energy. 



The so-called movements of the growing parts of plants 

 are frequently quoted in this connection. As we shall see 

 hereafter however these are usually changes of position 

 induced by variations in the processes of growth, and may 

 rather be referred to expenditure of energy in connection 

 with the latter than to actual movement. The movements 

 of adult organs are also effected by causes which corre- 

 spond in great measure to those which modify growth, 

 being generally brought about by such variations in the 

 turgescence of particular cells or groups of cells as those 

 upon which we shall see growth largely depends. In this 

 sense they are to be associated with modifications of the 

 hydrostatic tensions in the parts concerned. A certain 

 amount of expenditure of energy in the cells concerned is 

 however most probable, though it is uncertain how far 

 such changes as modify the resistance of the protoplasm to 

 the passage of water througli it involve the application of 

 energy. 



We have instances of what we may call the passive 

 escape of energy in the shape of heat, and to a less extent 

 in the manifestation of the so-called phenomena of phos- 

 phorescence. Heat is lost to the plant in many ways, one 



