Light reaction in lower organisms. II. Volvox globator

motion, but only.two of them, OLTMANNS and HOLMES, made a special study of the reactions of the organism.OLTMANNS ('92, p. 195) concluded that the difference in light intensity was the chief factor in determining the direction of motion, thus opposing the ray-direction'' theory of SACHS, and originating the contention concerning the efficacy of ray-direction and that of difference in light intensity in producing orientation.HOLMES ('03, p. 324) after a detailed discussion leaves the question in a very unsettled condition, as is indicated by the following statement: " T h e direction of the rays may be the i m p o r t a t factor in orientation irrespective of difference in intensity of light upon different parts of the organism as has been maintained by SACHS for the phototropic movements of plants."T h e ray-direction theory of SACHS is still supported by LOEB and the majority of botanists, but is opposed, on the one hand by HOLT and LEE and others who support the views of OLTMANNS, and on the other hand by the "motor reaction" theory of J E N N I N G S and his followers, who agree with OLTMANNS in holding that difference in light intensity is the cause of the reaction, but give a different account of how the reaction occurs.They hold, however, that difference in light intensity is functional in causing reaction only in so far a s such difference makes changes in intensity on the organisms possible.These theories are so well known that it will be sufficient to merely mention them here.