Law of Proenvironment 209 



an infinitesimally greater amount of oxygen on one side than 

 on another, of each bacterium, causes it to plot out a pathway 

 for itself that is accurately determined stage by stage according 

 to the relative amount of oxygen in its surroundings. 



Now, in the above case selected from the Acaryota, the 

 stimulus and the succeeding proenvironal response are alike 

 single, simple, and direct. The extreme delicacy of the stim- 

 ulus, and so of the perceptive response in this case, is proved 

 by Engelmann's estimate that the 100,000.000 of a milligram of 

 oxygen will suffice to start movement. So far also as we at 

 present know them physiologically, it seems true for many 

 of the Acaryota that their proenvironal responses are simple 

 and direct for each type of stimulus. But it may be that at 

 least the higher types, with rudimentary nuclear structures, 

 like Oscillatoria and many motile bacteria, may yet be shown 

 to have the power of perceiving and of compounding two or 

 more energizing stimuli, and thereafter of plotting an environal 

 pathway that is the resultant mean of these several stimuli, 

 and that will lead the organism along a satisfied resultant 

 environal course. 



Thus, if it could be clearly demonstrated in regard to Mas- 

 sart's experiments on gravitation movements of bacteria (80: 

 158) that these bacteria, when exposed to gravic stimulus in 

 one direction and to oxy-chemic stimulus in another, pursued 

 a pathway that was a resultant between the two stimuli, direct 

 proof of resultant proenvironal response would be secured. 

 A very wide field for experimental study is here open amongst 

 the Acaryota. An excellent summary of results already ob- 

 tained is given by Jennings (J^2: 37-40). 



Our knowledge of the unicellular Caryota is much fuller 

 and more exact. Their possession of a chromatin nuclear 

 and nucleolar mass evidently confers more complicated and 

 quickly adjusted capacity for linking together, and responding 

 to, two or more stimuli. The motile or zoogonidial stage of 

 such waterweeds as Sphcerella and Chlamydomonas are highly 

 favorable plant objects, while Euglena, StentoTy and Para- 

 mcecium are equally good animal forms. Reference has already 



