vi MOVEMENTS OF MYXOMYCETES 313 



contact with the moist object, so as to enable the whole mass 

 of the plasmodium to migrate on to it." On the entrance of 

 the plasmodia into the fructifying condition, positive hydro- 

 tropism gives place to negative ; the myxomycete quits the 

 moist substratum and creeps upwards on to the surface of dry 

 objects. 



2. Unequal- distribution of warmth in the substratum, and 



3. Unequal supplies of oxygen also cause locomotion in 

 the Myxomycete. 



4. Chemical substances soluble in water have a similar 

 action. Contact of the plasmodia on one side with solutions 

 of common salt, saltpetre, carbonate of potash, cause them to 

 withdraw from the dangerous spot, while infusion of tan, or 

 a dilute solution of sugar, produces a flow of the protoplasm 

 and ultimately translocation of the whole plasmodial mass 

 towards the source of nourishment. Some solutions have an 

 attractive or repulsive effect according to their degree of 

 concentration. 



5. Finally, they withdraw from light (negative helio- 

 tropism). 



With regard to the acceleration or definite direction of 

 movement produced entirely by stimuli, compare the follow- 

 ing: 



" The knowledge of the remarkably delicate reaction of the 

 plasmodia under external influences enables us to compre- 

 hend how these tender structures, destitute of every kind of 

 external protection, are able to carry on their existence. 

 The plasmodia which are not yet ripe for reproduction are 

 kept in the moist substratum by positive hydrotropism, 

 which is assisted by negative heliotropism. 



" But within the darkness and moisture of the substratum 

 the plasmodia by no means remain in one place, because the 

 differences in the chemical composition of the substratum 

 cause continual migrations. The plasmodia have the faculty 



