60 PLANT PHYSIOLOGY 



rough-and-tumble heroics of Baly's test tube experiments with 

 the marked smoothness of the processes of the photosynthetic 

 mechanism of the plant." 



Part Played by Light. — Many investigators have attempted 

 the formation of carbohydrates in vitro, replacing light by some 

 other form of electrical or chemical energy. Butlerow (1861), 

 using limewater as a catalyzer, obtained from trioxymethylene, 

 which is a polymer of formaldehyde, a syrup with a bitter-sweetish 

 taste. Loew in a similar manner produced from formalin a color- 

 less syrup, which he called formose, that will reduce Fehling's 

 solution. Lob, using a silent discharge as a source of energy, found 

 that carbon dioxide and water produced formaldehyde and in 

 addition carbon monoxide and hydrogen peroxide. These last two 

 products are especially interesting in the light of the work of von 

 Baeyer, Usher, and Priestley. The latter investigators found that 

 carbon dioxide and water, when placed in a quartz tube along with 

 an alkali and subjected to the rays of a mercury vapor light espe- 

 cially rich in the violet and ultra-violet rays, produce form- 

 aldehyde and even carbohydrates; but Stoklasa found that for 

 carbohydrate production nascent hydrogen must also be present. 

 The most important work in this field is that of Baly, described 

 above. 



Experiments such as these have led many to believe that the 

 light energy is in some way transformed into electrical energy; 

 but the boundary line between these two phases of energy seems in 

 certain regions of the spectrum to be especially indistinct. It is a 

 matter of common knowledge that light is a form of energy, that 

 it can be transformed into other forms, and that the plant is able 

 to transform this kinetic light energy into the potential energy 

 of carbon compounds. Light is able to decompose silver salts, 

 fade rugs, etc., and its decomposition or rearrangement of the 

 carbon dioxide molecule is no more strange. 



Part Played by Chlorophyll. — It was once thought that chloro- 

 phyll was an absorbing screen for gathering the rays of the orange- 

 red region which are most used in photosynthesis. Later it was 

 considered by some as a sort of sensitizer or catalyzer which per- 

 mitted the protoplasm of the chloroplastid to carry on the work 

 of photosynthesis. Bacteria when impregnated with eosin, a red 

 dye, are very sensitive to light and soon succumb, while in the 

 dark they are not affected ; and iu some such way, it was proposed 



