FOUR FIGURES
W e are investigating the structure of pliotorecr~ptors, tht. chloroplasts and retinal rocis in a variety of 1)lant arid anirrial material, and particulai*ly the structural cliaiiges accompany- ing the synthesis and bleaching of thc pigrrients during thc light dark reactions (Wollien and Palacle, '32, '53 ; 71Tolken antl Schwertz, 5 3 , and Wolken and Mcllon, '56).
S e w e r tcdiiiityucs in fixation aiici thin-~cctioning f o r clec.troii microscopy have shown that the chloroplasts from a VRriety of plant rnatcrial (Stcinman, '52, ',X ; I'alade, '53) antl the retinal rods of frog, guinea pig and perch arc lnminatctl discs whose thickness is the same order of iiiagnitutlc (Sjostrand, '49, 't537 and Ti'ern6ndez-iUoriin7 '<54).
Our studies by electron microscopy of osmium fisctl algal flagellates showed that the chloroplasts are composed of piledup discs o r plates, approximately 42 for Eugleizn and 20 for Yoteriochronioncis. These plates consisted of dense bands allproximately 230 , % in thickness with denser peripheries 60-100 1 % in thickness with less dense intcrspaccs 200-500 L -% in thickness. This laminated chloroplast structurc was forniccl only in photosynthesizing light-adapted organisms anti not in chemosynthesizing dark-adapted organisms. This structural arrangement together with the pigment analysis permitted a 1 Aided in part by grants m-aid from U. S. Public IIcaltll Service, Institute r\reuroiogicni lliseases and Blindness (B-397) ; the Sationnl ('ouncil to Coarbat Blindness, Inc. (la8-C) ; and The McClintic Endowment. 349 JOUIINAL O F CELLULAR A N D COMP4RATIVE PHYSIOLOGY, V O L . 48, S O 3 DECLXBER 1956 a pH of 9.2-8.6. * Nacconal NRSFanionic organic detergent-alkyl aryl sulfonate, Sational Aniline Division, Allied Chemical and Dye Corporation. Digitonin -( ,..jHooOm) -anionic detergent, D-58, Fisher Scientific Company.