December 24, 1915] 



SCIENCE 



915 



table are given the percentages of living plants 

 and of v?ilt-free plants of each variety sixty- 

 eight days after planting. Most of the living 

 plants that were diseased could be told by an 

 external examination, but for these results all 

 living plants were cut and examined for the 

 presence of the discolored fibrovascular 

 bundles. 



This table shows the comparatively greater 

 resistance of the wilt-resistant variety as com- 

 pared to the others, and it also shows the large 

 percentage of susceptible plants that could be 

 eliminated before setting in the field. 



Although the investigations on this method 

 are far from complete, it seems well at this 

 time to put it into the hands of other workers 

 with the hope that it may be found useful. 

 C. W. Edgerton 



Louisiana Agricultural Experiment Station, 

 Baton Eouge, La. 



do movements occur in the visual cells and 

 retinal pigment op man?^ 

 The statement is commonly found in text- 

 books of gross^ and microscopical anatomy, as 

 well as in some texts of physiology,* that the 



1 Contributions from the Zoological Laboratory 

 of the Museum of Comparative Zoology at Har- 

 vard College, No. 263. 



^ E. g., R. Howden, 1913, in Cunningham 's 

 "Anatomy," 4th ed., p. 817. E. A. Spitzka, 1910, 

 in Gray's "Anatomy," 18th ed., p. 1106. Pier- 

 sol, G. A., 1906, "Human Anatomy," p. 1463. 



3S. g., Bailey, F. E., 1913, "Text-book of His- 

 tology," 4th ed., p. 556. Piersol, G. A., 1913, 

 "Normal Histology," 10th ed., p. 348. 



*E. g., Halliburton, W. D., 1910, "Handbook 

 of Physiology," 9th ed., p. 843. Starling, E. H., 

 1912, "Principles of Human Physiology," p. 630 

 (by implication). 



retinal pigment of the human eye undergoes 

 positional changes in light and in darkness. 

 The pigment, which, in the dark, forms a com- 

 pact layer next to the choroid, is said to mi- 

 grate towards the external limiting membrane 

 in the light, thereby forming processes which 

 interdigitate with the rods and cones. If not 

 explicitly stated, it is at least implied that 

 this response is well marked and the actual 

 migration extensive. 



This view is so generally accepted as express- 

 ing a commonplace of retinal physiology that 

 it is well worth while to examine the facts 

 upon which its validity rests. 



That photomechanical changes take place in 

 the retinal pigment of anuran amphibians, a 

 fact first established independently by BolP 

 and by Kiihne^ on the frog in 1877, may be 

 substantiated by any one who will perform the 

 necessary experiments. Similar results, in 

 many cases even more striking, were obtained 

 on fishes (Stort, '86).' Angelucci ('78)8 Yik^. 

 wise first reported this condition to hold for 

 Triton as a type of urodele amphibian, and 

 Stort ('87),^ using the pigeon for material, 

 again presented the earliest demonstration in 

 the retina of birds. 



Wlien reptiles and mammals are considered, 

 on the other hand, the literature at once be- 

 comes contradictory. Angelucci ('90),^" how- 

 ever, reported a rather limited pigment migra- 

 tion in the retina of Testudo marina, and 

 Chiarini ('06) ^^^ also states that a distinct but 



5 Boll, P., 1877, Monatsier. d. Tc. prenss. Akad. d. 

 Wiss. zu Berlin, pp. 72-74. 



6 Kulme, W., 1877, Untersuch. a. d. physiol. Inst. 

 d. Univ. BeideXberg, Bd. 1, pp. 15-103, Taf. 1. 



7 Stort, A. G. H., Van Genderen, 1886, Bericht 

 uier d. IS. Versamm. d. OphtJial. Gesell. eu Heid- 

 elberg, pp. 43^9. 



8 Angelucci, A., 1878, Arch. f. Anat. u. Physiol., 

 Physiol Alt., pp. 353-386. 



9 Stort, A. G. H., Van Genderen, 1887, Arch. 

 ne4rland. d. Sci. exact et nat., Tom. 21, pp. 316- 

 386. 



10 Angelucci, A., 1890, Untersuch. z. Naturlelire 

 d. Menschen u. d. Thiere, Bd. 14, pp. 231-357. 



11 Ctiiarini, P., 1906, Arch. ital. de Biol., Tom. 

 45, pp. 337-352. 



