THE LAMINA 



363 



fact that they were looked upon sHghtly obHciuely, so that their larger 

 dimensions parallel to the surface of the chloroplast could contribute to 

 visibility. Anthoceros chloroplasts contain no visible grana; but a similar 



W^ 



Fig. 41. — a, Laminar structure of a grana-free Antho- 

 ceros chloroplast (microphotograph in ultraviolet light: 

 ^ = 27.5 m^; magnification X 1000) (after Menke 1940). 

 b, Laminar structure of a grana-carrying chloroplast (after 

 Menke 1940). . 



disintegration into laminae was observed also with the granular chloro- 

 plasts of other plants. Menke concluded that the grana are parts of the 

 lamina, in which certain components (e. g., the pigments) are accumulated. 



This concept was further strengthened 

 by observations in ultraviolet light and 

 under the electron microscope. Figure 

 41a shows a slice of a grana-free Antho- 

 ceros chloroplast photographed by ]\Ienke 

 (1940) in ultraviolet light. The struc- 

 ture of grana-bearing chloroplasts, ob- 

 served by Menke with slices from Selag- 

 inella grandis and Phaseolus multiflorus, 

 is represented in the schematic figure 

 41b. The strong absorption of grana 

 in the ultraviolet, revealed by this figure, 

 may be caused by chlorophyll or the ca- 

 rotenoids (c/. Vol. II, Chapter 21); but 

 other compounds, for example, nucleic 

 acid, may contribute to it. Photographs 

 in ultraviolet light of different wave 

 length could perhaps disclose the distribution of various ultraviolet ab- 

 sorbing compounds in the chloroplasts. 



> 



•4^ 



Fig. 42. — Edge of a chloroplast 

 of Nicotiana iahacum (X 10,000) 

 (after Kausche and Ruska 1940). 



