264 A. E. HILTON ON THE CAUSE OF REVERSING CURRENTS 



of pressure sensation, produced by the flow of liquids. These 

 remarks, although suggestive, are not very illuminative ; and I 

 have not, as yet, met with anything more definite on the 

 subject. 



At this point it is advisable to notice that the problem before 

 us is by no means the same as that presented by such phenomena 

 as the circulation observable in the bended hairs of the stamens 

 of Spider wort (Tradescantia), or the Cyclosis in certain water- 

 plants, of which Nitella and Vallisneria are typical examples. 

 In those instances, the movements continue in one direction. 

 The reversing currents of plasmodia call for a different ex- 

 planation ; especially in view of the fact that there are reasons 

 for regarding the Mycetozoa as of animal rather than vegetable 

 nature. 



In seeking the solution we desire, our task is simplified if we 

 select for critical investigation a single representative species ; 

 and as I have had better opportunity of studying the plasmodium 

 of Badhamia utricidaris than of any other, the descriptions which 

 follow are to be understood as referring to that species in par- 

 ticular ; but while specific details vary, the main principles no 

 doubt apply very generally to the whole group. 



Viewed with the naked eye, or a pocket-lens, a healthy 

 plasmodium of B. utricidaris is seen to consist of a slimy sub- 

 stance, about the consistency of cream, orange-yellow in colour, 

 but of no definite or permanent shape. The colour is simply 

 due to absorbed materials, the digestible portions of which are 

 in process of assimilation. The plasm itself, which in a pure 

 state is almost transparent, is a complex substance, only able to 

 carry on its activities while in a viscous condition ; that is to 

 say, in combination with water. Water does not dissolve plasm, 

 and there is a limit to the quantity which plasm can imbibe ; 

 but owing to the loose molecular structure of the plasm, the 

 absorption of water greatly relaxes it, and increases its mobility. 

 On the other hand, if there is so much water that a plasmodium 

 is swamped, and cannot get into contact with air, it becomes 

 congested and moribund, as if suffocated, which is probably the 

 case. The most suitable habitats, therefore, are the damp sur- 

 faces and furrows of rotting tree-stumps, bark, decaying leaves, 

 mosses, and woody fungi, because these furnish not only food, 

 but also a watery substratum on which the under parts of the 



