THE ENERGY OF THE PLANT 283 
Many of the humbler plants possess a considerable power 
of active movement or locomotion. Zoospores of many of 
the Alge 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 im 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 amceboid 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 Alge, 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 im 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 
