Tlfi: BOT. I NH ■. I / .V. I ( lAZLXE. [Yol . xxi. No. 250. 



afford nn instance of the latter ease. Both authors find in the 

 chemotaxis of the sperm at 020 ids of Pteridophyta that the 

 ring-collections with certain acids are the resultant of the at- 

 traction exercised by the anions and the repulsion due to the 

 cathions, H-ions. With Myxomyeetes a similar effect ex- 

 ercised by the acids can not be ascribed to the existence of 

 either optimal concentrations or two opponent components 

 exclusively. To know which of the two explanations may be 

 applicable we must first of all consider whether the acid used 

 is strong or weak. As has been stated above, the active com- 

 ponent of strong acids, namely sulphuric, hydrochloric, nitric 

 and oxalic acids, is exclusively H-ion. At the infra-optimal zone 

 of these acids the swarm-spores are stimulated by it to ap- 

 proach the optimal zone. At the supra-optimal zone is effected 

 the negative chemotaxis and the spores are driven back again 

 to the optimal zone which extends with sulphuric acid to 

 0.2-0. 25mm. on the average at the distance of 2-2. 5mm. from 

 the mouth of a tube containing 1 mol of the acid. The con- 

 centrated H-ions seem to be toxic upon the spores, for these 

 shrink in body, become less active and come afterwards to rest. 

 At the inner margin of the ring we observe that some spores 

 may often fall into such danger. 



Xow with weak acids. Take for example acetic acid. The 

 diameter of the ring formed by it is nearly equal to that 

 formed by strong mineral acids, so that it appears at once 

 that the zone of optimal concentration of H-ions may be at 

 nearly equal distance from the diffusion center, the mouth of 

 the capillary. Taking, however, its less dissociability into 

 consideration it must be admitted that the number of H-ions 

 should be far less in this case. The fact that the concentration 

 of the spores in the ring is not so dense as is the case with 

 strong acids indicates with cetainty a less quantity of H-ions. 

 Moreover, the diffuse collection at the outer margin of the ring 

 caused by Other weak acids must be ascribed to the infra- 

 optimal concentration of H-ions existing at the ring. The cotn- 

 ponent for repulsion is, therefore, not supra-optimal H-ions hut 

 certainly undissocia led molecules oi acids. 



