BIREFRINGENCE OF CHLOROPLASTS 367 



lipides with ether makes it negative. Thus, in living cells, the negative 

 morphic birefringence overcompensates the positive intrinsic birefringence 

 of the lipides, while the relation in dried chloroplasts is reversed, prob- 

 ably because of a distortion of the laminar structure. 



Strugger (1936) showed that the leaves of Elodea can be stained with 

 the lipophilic dyestuff rhodamine B, without affecting their vitality (as 

 shown by unimpaired photosynthetic activity). According to Menke 

 (1938), chloroi)lasts stained in this way exhibit a strong dichroism, whose 

 character indicates that the long axes of the lipide molecules are arranged 

 normally to the surface of the chloroplast. Thus, the laminae probably 

 consist of a forest of long molecules aligned parallel to the short axis of 

 the chloroplast. 



Pirson and Alberts (1940) could not fully confirm the observation of 

 Strugger that staining with rhodamine B does not impair the photo- 

 synthetic efficiency of Elodea. Gessner (1941) found that staining causes 

 no ill effect in the dark, but that a "photodynamic" injury occurs in 

 light absorbed b}- the dye. This light is not utilized for photosj-nthesis. 

 The respiration of stained algae is not affected. 



It has been suggested that the flat, two-dimensional construction is 

 carried consequently through the whole leaf, beginning with the blade, 

 through chloroplasts and grana, down to the submicroscopical laminae — 

 in the same way in which the elongated, one-dimensional construction 

 is carried through the whole stem, through single fibers down to the long- 

 chain molecules of cellulose. However, the two-dimension principle 

 certainly is absent from the structure of many algae, whose thalli are 

 cylindrical rather than flat. Similarly, the chromoplasts of many algae 

 are hollow spheres, or amoeba-like bodies rather than flat discs or bands. 

 It would be interesting to know whether chromoplasts of this type also 

 contain laminae. jMenke and Koydl (1939) mentioned that the chromo- 

 plasts of brown and red algae show a positive double refraction; this may 

 indicate the absence of laminar structure. 



At present, we cannot be sure whether any of the structural units 

 observed in photosynthesizing cells is indispensable for photosynthesis. 

 Chloroplasts are absent in blue-green algae; grana seem to be present in 

 plants of all phyla — including even the Cyanophyceae — but have been 

 found missing in some species and individuals. Lamina, which, according 

 to Menke, and Kausche and Ruska, are more important structural units 

 than the grana, have not yet been observed in the chromatoplasts of red 

 and brown algae, not to speak of their probable absence in the chromato- 

 plasm of blue algae and purple bacteria. 



The existence in chloroplasts of proteinaceous and lipoid laminae, and 

 of a regular arra.v of long-shaped, ether-solul)le molecules whose axes are 

 parallel to the plane of these laminae, was deduced by legitimate specu- 



