RESEARCH ON CHLOROPHYLL 121 



results he obtained showed that the maximum activity 

 took place in the brightest region of the spectrum ; no 

 decompositioi/ of carbon dioxide occurred under the 

 more refrangible rays nor under the dark heat rays. 



Another investigator, Garreau, did considerable service 

 in 1849 and 185 1 by determining the relative values of 

 the upper and under surface of the leaf as paths of gaseous 

 exchange, more especially directing his attention to the 

 exhalation of water vapour. In 1838 BerzeUus and 

 also, in 185 1, Verdeil made attempts at isolating pure 

 chlorophyll. The latter treated a hot alcoholic extract 

 of leaves with Hme water and then added strong hydro- 

 chloric acid. The research in itself was of little or no 

 importance, but I mention it as many experimenters 

 from that day onwards strove to extract the pigment in a 

 pure condition by the use of reagents of the most drastic 

 character, ignoring the likehhood of the manufacture 

 thereby of decomposition products from so complex and 

 unstable a substance during extraction and purification. 



The only other paper in relation to chlorophyll I need 

 refer to is one by Gris who, in 1857, showed that seeds 

 which contained Httle or no iron, if grown in a medium 

 free from that metal, produce only a few partially green 

 leaves, and that subsequent leaves are quite chlorotic, 

 but that if a few drops of a solution of an iron salt be 

 added to the culture and if transpiration be active, these 

 chlorotic leaves become green in a few days. This result 

 gave rise to the behef that iron was an essential con- 

 stituent of chlorophyll, a view, however, that was after- 

 wards found to be incorrect. 



The Foundations of Palaeophytology 



There is one other department of botanical research 

 to which I have not as yet referred at all, viz., palaeo- 

 botany. Although the study of fossil plants is of 

 comparatively recent growth, the classical writers were 



