182 S. O. MAST 



WAVE LENGTH AND STIMULATION 



The effect of wave-length on stimulation was only super- 

 ficially investigated, but the results obtained indicate clearly 

 that the longer waves of light have a much higher stimulating 

 efficiency in the tadpoles of Amaroucium then they do in Volvox, 

 Pandorina, and other similar organisms. 



The tadpoles of Amaroucium constellatum were found to 

 orient fairly precisely in light from a 25-watt tungsten ruby 

 lamp at 100 cm, distance passed through two plates of ruby 

 glass and a fairly heavy sheet of tissue paper. In Volvox and 

 Pandorina, on the other hand, no responses whatever were ob- 

 served in light direct from the same lamp without any obstruc- 

 tion even at 5 cm. distance. Since these are quite as sensitive 

 as the tadpoles to white light, it is evident that the tadpoles are 

 much more sensitive to red than Volvox and Pandorina. 



DISCUSSION 



Among the various factors functional in the process of orien- 

 tation the character of the orienting response and its relation 

 to the stimulating agent is one concerning which there is at 

 present much contention. 



Is orientation due to a series of shocks or trigger reactions of 

 the ' all-or-none ' type dependent upon the time-rate of change 

 in illumination and bearing, only in so far as the threshold is con- 

 cerned, a definite quantitative relation to the energy received; 

 or is it due to reactions which themselves bear a definite quantita- 

 tive relation to the energy received, reactions, which are not 

 dependent upon the time-rate of change in illumination and in 

 which there is nothing in the nature of a threshold? This sort 

 of reaction has been referred to as a reaction to constant stimula- 

 tion. It seems to hold within a limited range in some of the 

 plant structures, e. g., certain plumules (Arisz, '11 and '15), and I 

 am inclined to think that it may hold for Eudendrium (Mast, 

 '11, p. 163; Loeb and Ewald, '14; Loeb and Wasteneys, '17) 

 and for other sessile forms in which orientation is irreversibly 

 fixed, but I hold that the evidence presented by Loeb, Garrey, 

 and others in favor of this view in so far as it concerns other 

 animals is inconclusive. 



