452 The Physiology of Plants BOOK in 



question in 1865 and 1867, and observed the details with 

 greater completeness. Frank took the subject up in 1872 

 and determined that the changes of position are directly 

 referable to the variations in intensity of insolation. His 

 observations showed that in very brilliant sunlight the 

 plastids retreat to the most shaded corners of the cells, 

 while in a moderate light they post themselves in positions 

 favourable to catching the incident rays. Frank termed 

 the two positions apostrophe and epistrophe respectively, 

 and showed that they are taken up in virtue of move- 

 ments of the protoplasm in which the plastids lie. He 

 noted that the collection of them in any particular position 

 is accompanied by a certain massing of the protoplasm in 

 such spots. In 1876 Micheli stated that the chloroplasts of 

 palisade parenchyma bulge inwards away from the cell wall 

 in moderate light, but flatten themselves against the wall 

 if the light is strong. The subject was studied with more 

 minuteness by Stahl in 1880. His results confirmed and 

 extended those of Frank, but he differed from the latter in 

 thinking the changes are made in obedience to the direction 

 rather than the intensity of the light. He found that the 

 cells of the leaves of Oxalis and those of Ricinus exhibit 

 the changes in a very marked manner, but he said that it 

 is not at all a general phenomenon in leaves, that in most 

 plants the palisade cells do not show it. He noticed that 

 the elongated band-like chloroplast of the cell of Meso- 

 carpus is affected by light in a similar way, twisting on its 

 axis so as to present its edge to very brilliant and its side 

 to moderate illumination. 



Haberlandt published researches on the same subject in 

 1886, in which he confirmed and extended Stahl's results. 



Light was shown to affect the more lowly plants also. 

 Baranetzky showed in 1876 that the plasmodia of the 

 Myxomycetes move away from it. Deleterious effects of 

 strong insolation were observed by very many botanists. 



