•">4 Livingston : Chemical stimulation of a green alga 



It would be unnecessarily increasing the bulk of literature to 

 attempt a discussion of the discrepancies between the different 

 series at hand. It is almost certain that the present lively activity 

 of physiologists in this regard will soon unearth additions to our 

 knowledge of the facts which will be vastly more valuable than 

 any amount of the older-fashioned a priori discussion of all the 

 conceivable possibilities of the case. The writer hopes in the near 

 future to study in a similar manner the influence of anions and of 

 certain organic poisons upon this organism. 



Summary 



The important results here described may be briefly stated as 

 follows : 



i. Nitrate and sulfate, in the case of a large number of metallic 

 elements, act in the same way and at the same concentration upon 

 the filamentous form of this alga. According to the theory of dis- 

 sociation, we conclude that the stimulation is due to the cations. 



2. At high enough concentrations death is produced. 



3. At somewhat lower concentrations most of the cations pro- 

 duce a change in form of the cells and in the manner of cell divis- 

 ion, which is strictly parallel to the change brought about by 

 extraction of water or inhibition of its absorption. 



4. Often at the same concentration as that mentioned in (3), 

 and in most cases at a strength somewhat lower than this, there 

 is a marked acceleration in the production of zoospores. This is 

 exactly the opposite of what results from water-extraction. 



5. The acceleration in zoospore activity gradually decreases 

 with weaker solutions of the poison until the normal behavior of 

 the filamentous form is reached. 



6. In general, the relative degrees of toxicity of the metals 

 here studied follow the order of those studied by other workers 

 with different organisms. But there are many unexplained dis- 

 crepancies. 



The Desert Botanical Laboratory of the 



Carnegie Institution, Tucson, Arizona, Aug. 5, 1904. 



