THE CHEMISTRY OF PHOTOSYNTHESIS 295 



Later Bokorny ^■' reported the formation of starch from a 0.001 per 

 cent formaldehyde sohition, but it is not absolutely certain from these 

 experiments whether the starch was actually formed from the formalde- 

 hyde or from sugar already present in the plants.*'^ Treboux **' found 

 that 0.005 per cent formaldehyde was poisonous to Elodea, while in a 

 0.0005 to 0.001 per cent solution the plants remained uninjured. How- 

 ever, Treboux could not detect any starch formation from formaldehyde 

 in the dark nor in the light in absence of carbon dioxide. That these 

 very dilute solutions of formaldehyde had not affected the photosyn- 

 thetic apparatus is proven by the fact that when the plants were exposed 

 to sunlight and carbon dioxide was added to the solution, starch appeared 

 in the chloroplast within 1-2 hours. 



An advance in the method of studying the problem . was made by 

 Grafe,®^ who used land plants, supplied the formaldehyde in gaseous 

 form and protected the roots. Under these conditions formaldehyde 

 could be tolerated to about 0.04 per cent in the air when the plant 

 was illuminated, but toxic effects became noticeable in the dark and in 

 the colorless portions of the plants. Definite conclusions as to whether 

 formaldehyde is used by the plants cannot be drawn from these experi- 

 ments. An increase in the size and development of the formaldehyde 

 cultures in the light as compared with the controls free from carbon 

 dioxide was probably the main result. Another interesting observation 

 was that the formaldehyde cultures contained no starch but a great deal 

 more of the reducing sugars than the plants grown normally. 



Miss Baker ®^ studied the effect of formaldehyde on the development 

 of seedlings in the light, i.e. from the germination of the seed through a 

 development of 22 to 28 days. She found that in the cultures in light 

 there was a smaller decrease in the dry weight of the seedlings when 

 formaldehyde was present than without this gas. She speaks of this as 

 an "increase in dry weight'" ; it is questionable whether this is justifi- 

 able. In the formaldehyde cultures there was never a gain in dry weight 

 over that of the original weight of the seed. This occurred only in 

 the presence of carbon dioxide. This becomes clearer from the follow- 

 ing example of one experiment. The seeds used were White Mustard, 

 temperature 14 to 25°, "amounts of formaldehyde in air, about 0.52 

 per cent, or about fifteen times as much potential carbon as is present 

 in normal air of 0.04 per cent of carbon dioxide." The duration of the 



experiment was 24 days : 



Orig. Dry 

 Atmosphere Weight 



Air — CO2 -I- CH.O 0.4015 gram 



Air — CO2 0.3985 



Air + CO2 0.3965 



*' Bokornv, Biochcm. Zcit.. 36, 92 (1911). 



""Bouilhac, Compt. rend., 135. 1369 (1902). 



"Treboux, Flora., 92, 7i (1903). 



■^Grafe and Viser, Ber. bot. Gcs.. 27. 431 (1909); 29, 19 (1911). 



*' Baker, Ann. Bot., 27, 411 (1913). 



