bo ALDEHYDES 



by examining a section of the leaf which has been dipped in 

 absolute alcohol. Formaldehyde is the only aldehyde giving 

 a stable red colour with the above reagent, but other aldehydes 

 give unstable green, yellow, or reddish-brown colours. 



Occurrence in the Plant. Since the work of Reinke, many 

 have reported the occurrence of formaldehyde in the plant,* 

 and its presence has been accepted as evidence of the truth of 

 Baeyer's hypothesis of photosynthesis. Recent investigations, 

 however, show that this formaldehyde is a degradation product 

 of chlorophyll. Ewart'sf conclusion that chlorophyll contains 

 formaldehyde in a combined state has been confirmed by 

 Schryver, ;; who has published certain observations on the sub- 

 ject. He finds that formaldehyde is more abundant in chloro- 

 phyll films after exposure to bright sunlight than when ex- 

 ' posed to a dull light He also states that if glass plates 

 covered with films of chlorophyll be kept in the dark no 

 formaldehyde is produced, no matter whether moist carbon 

 dioxide be present or not ; further, if such plates be exposed 

 to sunlight in an atmosphere free from carbon dioxide, a very 

 minute quantity of formaldehyde is produced ; on the other 

 hand, the plates when exposed to the sun's rays in the presence 

 of moist carbon dioxide give a distinct formaldehyde reaction. 



From this Schryver concludes that in the presence of sun- 

 light, water, and carbon dioxide, there is a continuous pro- 

 duction of formaldehyde, which is continually being condensed 

 to sugar. If this condensation does not proceed rapidly 

 enough to remove all the formaldehyde, the excess enters into 

 combination with the chlorophyll, and, as the free formalde- 

 hyde is used up, this compound of formaldehyde with chloro- 

 phyll decomposes, setting free the former, which is converted 

 into sugar. There is thus in the plant a mechanism by means 

 of which the quantity of free formaldehyde is regulated, so that 

 at no time is the amount sufficiently large to become toxic. 



*Curttus and Franzen : " Ber. deut. chem. Gesells.," 1912, 45, 1715; 

 Reinke: "Ber. deut. hot. Gesells.," 1883, I, 406; Curtius and Reinke: " Ber. 

 deut. chem. Gesells.," 1897,30, 201; " Sitz. Heidelberger Akad. Wiss. Math. 

 Nat.," 1915 Abt. A. ; Pollacci : Atti. Inst. Bot. Pavia.," 1900,6, 1902, 8, 1904, 

 10 ; Usher and Priestley : " Proc. Roy. Soc., Lond.," B., 1906, 77, 369. 



fEwart: "Proc. Roy. Soc., Lond.," B., 1908, 80, 30. 



% Schryver : id., 1910, 82, 226. 



