68 ALDEHYDES AND ALCOHOLS 



with various gases, to light, they found that formaldehyde was 

 only produced in the presence of oxygen. In the case of con- 

 tact with carbon dioxide, phseophytin (see p. 319) was pro- 

 duced, and there was no further change. In oxygen the 

 chlorophyll turned yellow, due to the presence of phaeophytin, 

 and ultimately was bleached ; when the bleaching is in pro- 

 gress, formaldehyde occurs in but small quantity, but when the 

 bleaching is complete, there is an increase in the amount of 

 formaldehyde. They suggest that the formaldehyde arises 

 chiefly from the phytol which probably is split off from the 

 chlorophyll under the action of light and oxygen. 



In conclusion, mention may be made of a simple way of 

 demonstrating the production of formaldehyde from chloro- 

 phyll, due to Osterhout.* 



A solution of chlorophyll is made with carbon tetrachlor- 

 ide, and in it filter paper is soaked. The filter papers are 

 dried, moistened with water, and placed on the inner surface 

 of a glass bell-jar. The bell-jar is inverted over a dish of 

 water, sealed from the air, and exposed to sunlight. The 

 chlorophyll papers are gradually bleached ; when pale green 

 in colour the water in the dish gives a positive reaction for 

 aldehyde. The same result was obtained when the carbon 

 dioxide was excluded or increased to 10 per cent, which indi- 

 cates that the aldehyde is due to the colouring matter rather 

 than the carbon dioxide. Like results obtained when various 

 aniline dyes, notably methyl green and iodine green, were 

 used in place of the chlorophyll. 



To summarize, while there is much experimental proof 

 for the presence of formaldehyde and higher aldehydes in 

 plants, this is not evidence in support of the formaldehyde 

 hypothesis of carbon assimilation, since it has been repeatedly 

 shown that formaldehyde is produced by the decomposition 

 of chlorophyll itself. The whole question is considered in 

 greater detail in the second volume. 



* Osterhout : " Amer. J. Bot.," 1918, 5. 5"- 



