Nov. 1907.] KUSANO.—PHOBO-CHEMOTAXIS OF MYXOMYCETES. 151 



Both positive and negative chemotaxis of the swarm-spores 

 of Myxomycetes are typically phobotactic. 1} They react to a 

 decreasing concentration and are passively collected at a higher 

 concentration of stimulants. So that an easy or difficult 

 collection near the mouth of the tube filled with attractive 

 substances is dependent upon a larger or smaller area of 

 diffusion-zone as well as upon a greater or smaller difference of 

 concentration at the successive zones. The larger the area of 

 the zone the more the spores enter it at random, and, if the 

 difference of concentration at the successive zones is more sharp 

 they can reach more frequently, during their swimming, repellent 

 zones, in a given time, and can be drawn together more rapidly 

 towards the source of stimulation. If, on the other hand, the 

 difference is very small, in spite of the existence of a sufficient 

 quantity of stimulating substances in the diffusion-zones, the 

 swarm-spores will evince only the least inclination to enter the 

 zone of higher concentrations, or to approach the source of 

 stimulation. It may be permitted, therefore, to state that an 

 apparent collection near or in the tube with stimulating 

 subatances is by no means a necessary effect of the phobo- 

 tactic reaction. In fact, the non-attraction of hydrochloric 

 and nitric acids less than 1/200-1/300 mol does not show the 

 insensibility of the swarm-spores, but merely points out their 

 difficulties in finding out a chance to enter the tube or to 

 approach its mouth, which might be caused by the slight 

 difference of the concentration of acids at their diffusion-zones. 



Basing on this reason, we are led to think that, in the 

 phobo-chemotactic experiment, it is less advisable to apply, as 

 in the topo-chemotaxis, the usual capillary method in the de- 

 termination of the minimal stimuli (" Schwellenwerte ") with 

 chemical substances. It seems to me that the following method 

 is, so far as Myxomycetes are concerned, more profitable. A 

 comparatively large capillary tube is filled with swarm-spores 

 by capillary action and, after one end of the tube has been 



i) Pfeffer, loc. cit. p. 755. 



