120 HISTORY OF BOTANY 



decomposition under different conditions by counting 

 and analysing the gas bubbles given off by submerged 

 plants in sunlight. In 1838 Von Mohl made the first 

 serious attempt to elucidate the nature of the chlorophyll 

 apparatus. He showed that the pigment did not occur 

 in solution in the cell but existed in the form of minute 

 green viscid masses of varied shape, and proved the 

 presence in them of granules of starch by treating the 

 tissue with iodine solution. It should be remembered 

 that Grew spoke of chlorophyll as a " green precipitate," 

 so that the solid condition in which the pigment existed 

 in the cell was not altogether a new discovery. Further, 

 the " gas bubble " method of determining the activity 

 of carbon dioxide decomposition first employed by 

 Dutrochet is usually credited to Sachs, as is also the 

 identification of starch granules in chloroplasts by the 

 iodine test. It is remarkable that in the prominent 

 textbook of the period, the Grundzuge of Schleiden, all 

 the work of Ingen-Housz, De Saussure, Dutrochet, and 

 others I have mentioned, is completely ignored or flatly 

 contradicted. On this particular question of carbon- 

 assimilation Schleiden shows himself retrogressive in the 

 extreme. " Thus it appears," he writes, " at least as far 

 as the facts carry us, to be completely proved that plants 

 are not nourished by the carbonic acid of the atmosphere 

 by aid of their green parts " (auf diese Weise scheint, 

 wenigstens soweit bis jetzt die Thatsachen vorliegen, 

 vollkommen festzustehen, dass die Pflanzen sich nicht 

 auf Kosten der Kohlensaure der Atmosphaere durch die 

 griinen Theile nahren). 



While Daubeny used coloured glass screens in his 

 experiments Draper employed the spectrum itself. He 

 placed leaves of various plants in water impregnated 

 with carbon dioxide and submitted them to the rays 

 from different parts of the spectrum and estimated the 

 activity of decomposition by measuring the amounts of 

 oxygen given off, with the aid of an eudiometer. The 



