THE ENEEGY OF THE PLANT 283 



Many of the humbler plants possess a considerable power 

 of active movement or locomotion. Zoospores of many of 

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

 other 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 compared with 

 the total amount which they possess. Other movements 

 which are not dependent upon ciliary action are not un- 

 common. 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 movements of diatoms and the oscillations of certain 

 filamentous Algse, 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 correspond 

 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 through it involve the application of energy. The 

 establishment and maintenance of the turgid condition, 

 due to the hydrostatic distension of the extensible cell-wall, 

 also demands the expenditure 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 



