SPECTRAL COLOR AND STIMULATION 511 



flatter than those representing the results obtained with Eu- 

 glena or with Chalmydomonas. In Euglena the effective re- 

 gion extends approximately from 420 to 520 fxfj., while in Pan- 

 dorina it extends approximately from 440 to 620 (x/jl. And 

 the region of maximum stimulation for Pandorina, which is in 

 the green in the neighborhood of 524 fxn, nearly coincides with 

 the upper limit of the effective region for Euglena; so that the 

 stimulating efficiency for Euglena is practically zero in the re- 

 gion which has the highest stimulating efficiency for Pandorina. 



By comparing the last three columns in table 10 with the three 

 preceding columns it will be seen that while the region of maxi- 

 mum efficiency is, as previously stated, near 524 /x^ the region 

 of maximum effect is near 544 ix/x. That is, the correction for 

 unequal distribution of energy and dispersion in the spectrum 

 resulted in a considerable shift of the maximum toward the 

 blue, a much greater shift than similar corrections produced in 

 Euglena. This is, of course, due to the fact that in the former 

 the region of maximum stimulating effect is nearer the red than 

 in the latter. Further reference to these tables and to figure 4 

 will also indicate that, just as in Euglena, a change in the sense 

 of reaction does not alter the relative stimulating efficiency of 

 the spectral colors; it appears to be the same regardless as to 

 whether they are positive or negative. 



The conclusion reached on the basis of the results of the three 

 series of tests given in table 10 are in the main supported by the 

 results obtained in practically all of the other series of tests 

 made, a total of 24, Many of these series, however, were limited 

 to the region of the spectrum extending but a short distance on 

 either side of the maximum and the results obtained in them 

 consequently bear primarily on the question as to the location 

 of this point. 



By referring to table 10 it will be seen that the point of maxi- 

 mum stimulating effect in all of the three series of tests recorded 

 lies near wave-length 544 fin. In 11 of the 24 series not re- 

 corded in this table it was found to be in practically the same 

 place as in those recorded in the table, in 9 somewhat nearer 

 554 nn, in one very near 564 /x^t and in the remaining 3 somewhere 



