146 ON THE POWER OF MOVEMENT IN PLANTS. 



molecules in motion, and representing an amount of ' work ' that 

 is often enormous. Starch, for instance, in dry grains absorbing 

 water of the same temperature, will cause a rise of 2° or 3° C, 

 while boiling water is only raised 0*078° C. by a pressure of ten 

 atmospheres. Absorption of water alone then means the develop- 

 ment of an enormous force. 



Te?isio?i of Tissues or cells due to unequal growth of layers 

 is another cause. 



Tiirgidity, or pressure of cell-sap on the cell-wall, does its share 

 in promoting motion by disturbance of equilibrium, turgidity being 

 caused by attraction of water by the substances dissolved in the 

 cell-sap. 



Diffusion of Gases assists in the general bringing about of 

 motion. 



Light and Heat play an important part in the same direction, 

 as is well seen in the action of these agents on chlorophyll grains 

 and Algce spores, causing them to visibly shift their positions. 



So we may see evidence of the transformation of light and 

 heat into energy and motion, and the law of the correlation of 

 physical forces finds here abundant illustration. 'Heat as a mode 

 of motion ' can be said to find expression in the phenomenon of 

 movement in cell-contents. 



B. — Motion of Naked Cells, or Primordial Cells. . 



If protoplasm confined by a cell-wall can show such activity, 

 we can very easily imagine that when not so enveloped, it might be 

 able to move of its own accord fro7n one place to a7iother. This 

 actually occurs in the abnormal group of Fimgi called Myxo7nycetes. 

 For instance, take j^thaliimi or 'flowers of tan,' an orange- 

 coloured organism growing in and around tan-pits. It exists as a 

 Plasmodium^ a mass of protoplasm with no cellulose wall, slimy or 

 creamy in appearance, and made up of a number of anastomosing 

 net-like channels, along which a pretty constant current of proto- 

 plasm passes, carrying all kinds of foreign bodies with it. This 

 Plasmodium moves slowly but freely from place to place by project- 

 ing at its edge a number oi pseudopodia, or arm-like processes, into 

 which this current of moving protoplasm flows, thus increasing 

 their size ; this has only to persist for a time, and the whole mass 



