LIFE AND LIGHT 25 



deposited instead of starch granules in the plastids. Also the plastids 

 and the cells containing them multiply rapidly, and for this purpose 

 utilise the solar energy given to them, there being no proof that the 

 materials first formed must visit roots or other organs of the plant 

 before being converted into proteins to meet this plastid production. 

 Most of the nitrogen entering the leaf enters it in the form of in- 

 organic salts, and is transformed into protein nitrogen in the leaf. 

 This misconception that carbohydrate must first be formed before 

 fats or proteins can arise is based upon no clear experimental 

 evidence, but upon a series of ingenious but rather unsuccessful 

 attempts to demonstrate the first steps of photo- synthesis. 



The most popular idea regarding the first step is that first pro- 

 posed by A. von Baey_eji viz., that formaldehyde is formed by union 

 of carbonic acid and water under the influence of the input of light 

 energy somewhat in this fashion : 



/OH 



CO., + H.,0 = OC< (carbonic acid) 

 >OH 



/OH /H 



OC/ + 2H-OH = OC< + 2HO-OH 



-OH \H 



(carbonic acid) (water) = (formaldehyde) + (hydrogen peroxide) 



or, if written in shortest form, so as to express the net result : 



It is quite possible by juggling with the formulae of organic 

 chemistry to write many dozens of such equations, and to show the 

 possibility on paper of the formation of hundreds of organic 

 substances other than formaldehyde ; but the real question is, Do 

 such reactions occur in the cell ? 



Formaldehyde is a substance for which many delicate reactions 

 exist capable of showing extraordinarily minute traces of aldehyde, 

 and these reactions have been most ingeniously applied to show that 

 minute traces of formaldehyde exist in the green leaf and in increased 

 amount after active photo- synthesis. 



The defect of all these reactions for aldehyde is, in the first place, 

 that they are too delicate, and, in the second place, that they may be 

 given by other aldehydes than formaldehyde, and by other organic 

 products of cellular metabolism. Further, even admitting that the 



