170 PHOTOSYNTHESIS 



photosynthesis problem requires still a great deal more investigation before 

 any definite conclusion can be arrived at. 



Finally, as internal factors which affect the rate of photosynthesis 

 there come into play the position of the chloroplasts, the accumulation and 

 translocation of the material synthesized. These are discussed in the 

 sections devoted to chloroplasts and to the time factor. 



i. Effect of Various Substances, of Age, Electricity, etc. 



It has long been a question vi^hether other substances could be substi- 

 tuted for carbon dioxide in the photosynthetic process. There are a num- 

 ber of substances which when fed to plants produce starch, but most of 

 these are of practically an equal energy content as hexose sugars, so that 

 radiant energy is not necessary and the starch formation is not a photo- 

 synthesis. We are concerned first with those substances which require 

 reduction, in which the reaction step to sugar is endothermic and hence 

 would require the absorption of energy. The first to suggest itself in this 

 relation is the lower oxide of carbon. 



Carbon monoxide: de Saussure found that the behavior of plants in 

 this gas is the same as in an atmosphere of nitrogen. ^^^ There were no 

 evidences of photosynthesis. Virtually the same conclusions were arrived 

 at by Boussingault'^^^ and by Stutzer.^oo Richards and MacDougaP°^ 

 found that larger quantities of carbon m.onoxide are toxic for phanerogams. 

 Krascheninnikofif also found that it could not be used, while the results 

 of Bottomley and Jackson -''- indicate that this gas can, to a measure at 

 least replace carbon dioxide in photosynthesis. Recently Wehmer ^^^^ has 

 reported that carbon monoxide up to a concentration of 50 per cent exerts 

 no injurious effect on the development of seedlings. 



Formic Acid: Usher and Priestley 2°* report the formation of oxygen 

 from Elodca in 0.02 per cent solution of this acid, on illumination. 

 Spoehr ^o^ has also found that in an atmosphere containing small quantities 

 of formic acid but no carbon dioxide, leaves of the sunflower show an 

 appreciable gain in dry weight and form starch in bright sunlight. Plants 

 cannot endure high concentrations of this acid, and in the dark the toxicity 

 soon becomes evident. 



Ketene, CH2 : CO, and Carbon Suboxide C3O2, have as far as we 

 know not been investigated and on account of their poisonous and reactive 

 properties probably offer little of interest. Collie '°« suggested that deriva- 



"'Ostwald's "Klassiker d. Exakten Wissenschaften," No. 16, p. 27. 

 ""' Boussingault, "Agronomic chimic agricole," etc., 4, 300 (1868). 

 ''" Stutzer, Ber. chcm. Gcs., 9, 1570 (1876). Just, IValhiys Forsch. Agnk. pliysik., 

 5 79 (1882). Krascheninnikoff, Rev. gen. bot.. 21, 173 (1909). 



*"' Richards and MacDougal, Bull. Torrev Bot. Club, 31, 57 (1904). 



="' Bottomley and Jackson, Proc. Roy. Soc, 72, 130 (1903). 



='"' Wehmer, Ber. bot. Gcs., 43, 184 (1925). 



==»' Usher and Priestley, Proc. Rov. Soc, 78 B, 322 (1906). 



'"•^Spoehr, Plant World, 19, 15 (1916). 



^Collie, Jour. Chcm. Soc, 91, 1806 (1907). 



