3 CHLOROPLASTS 255 



detected as yet. When such a chloroplast is fixed in Zenker's solution, 

 picric acid/HgCL, or Flemming's solution and is then observed in 

 mixtures of acetone and methylene iodide with refractive indices // 

 increasing from 1.36 to 1.74, the birefringence changes following a 

 hyperbolic curve. According to Wiener's theory of the anisotropy of 

 composite bodies, this behaviour discloses a layered structure (Fig. 

 60b, p. 82), the lamellae of which are thin compared with the wave- 

 lengths of light. When the imbibition is made with a mixture of 

 fj = 1.58, the chloroplast becomes isotropic. This is the point where 

 the lamellae have the same refractive index as the imbibing medium. 

 As acetone removes the lipids, the disclosed lamellae must consist of 

 protein. It is of interest to note that muscle protein and neurokeratin 

 from nerve sheaths also have a refractive index as high as i . 5 8 (Schmidt 

 1937b). 



If the chloroplasts are fixed with OsO^, the lipids become partly 

 insoluble. Then we find, in addition to the variable layer birefringence 

 mentioned above, a constant intrinsic anisotropy, independent of the 

 refractive index of the imbibition medium, which is due to orientated 

 adsorbed lipids (Fig. 129). Thus, the chloroplast of Mougeotia has a 

 submicroscopic layered structure of protein and interposed orientated 

 lipid lamellae. In Menke's experiments (1934b) with chloroplasts of 

 Closterium the lipids produced myelin forms which, like lecithin, 

 sodium oleate, etc., are optically positive with reference to the radius 

 of the tubes. From this it follows that the orientation of the lipids 

 in the plastids must be as shown in Fig. 130a (L). 



At first, Menke (1938c) regarded the proposed scheme (Frey- 

 Wyssling, 1937c) of the lamellar fine-structure of chloroplasts with 



p .■.• ■ ■.■.■.-■■/..'•• 



t mmiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii 



p .-'.■.. -'..■■.■..•.-:-■■■.■: ■■■ 



f Tnnriiii iiiiiiiiiiiiiiiiiiiiiiiiiiiiiin':;iiiiiiii 



p ' ■' .•.■.•..•. 



L Mnn iiiii iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii l>) 



p //!■.■'■-•.■.■-■.■.•.•.■■."■■■■ 



^) 



Fig. 130. Structure of chloroplasts. a) Submicroscopic layer structur neglecting the grana 

 structure. P protein layer, L lipid layer, with indication of the optical character (from Frey- 

 Wyssling, 1937O; ^) scheme of a cross-section of a chloroplast in ultraviolet light 



(from Menke, 1940^). 



