294 PHOTOSYNTHESIS 



leaves, or only the slightest traces, it can safely be assumed that this 

 substance does not accumulate to any extent. Compare to this the method 

 of bathing the entire plant (in case of an aquatic plant) in a formalde- 

 hyde solution or exposing a leaf, with its delicate stomatal mechani>m. 

 to gaseous formaldehyde, a notoriously poisonous substance, and the 

 difference in the two sets of conditions must be evident. Consequently 

 too much is not to be expected from the physiological experiments of 

 this nature, for on the one hand, negative results with a certain sub- 

 stance may simply mean that it has not been supplied at the proper 

 concentration, that it does not penetrate to the proper locality in the 

 cell or that some other accessory factor has not been supplied, etc., while 

 a positive result, on the other hand, may still mean very little toward 

 establishing the substance fed as an intermediate product, for we know 

 of a variety of substances from which the plant is capable of produc- 

 ing sugar and starch, but which for obvious chemical reasons we do not 

 consider intermediate products of photosynthesis. 



a. Formaldehyde. 



Feeding experiments with formaldehyde have been carried out for a 

 great many years and much has been written regarding the results ob- 

 tained and the methods which must be followed.**- The poisonous prop- 

 erty of formaldehyde was recognized as a factor to be guarded against, 

 wherefore compounds of formaldehyde were first used which in water 

 solution produced only very small concentrations of this substance. Thus 

 methylal, CH^.(OCH3)o, was at first used, though it was later realized 

 that the methyl alcohol, which is simultaneously produced with formalde- 

 hyde from methylal, is capable of producing starch in spirogyra. 



Similarly, the addition product which formaldehyde forms with sodium 

 bisulfite was used.®^ The slight increases in weight and the decrease in 

 reducing power of the solution in which the plants were placed are not 

 satisfactory criteria from which a utilization of formaldehyde can be 

 concluded. 



Positive results under these conditions and by using pure formaldehvde 

 solutions were claimed for algae when exposed to the light, but not when 

 in the dark. The decrease in the reducing power of the formaldehyde- 

 sodium sulfite solution may well have been due to oxidation of the 

 formaldehyde. Schroeder ®* also considers that an increase in weight 

 may be ascribed to the action of bacteria which may convert the formalde- 

 hyde into other organic compounds which the algae are capable of 

 assimilating. 



*'' Bokorny, "Studien u. Experimente ii. den chemischen Vorgang der Assimila- 

 tion," Erlangcn, 1888. Bcr. bot. Ges., 6, 116 (1888). Loew and Bokorny, Jour, 

 prakt. Chcm., 36, 285 (1887). Bouilhac, Compi. rend., 133, 751 (1901). 



"Bokorny, Ber. bot. Ges.. 9. 103 (1891) ; Landzc. Jahrh., 21, 445 (1892) ; Arch, 

 f. Hyg., 14, 202 (1892) ; Pfliiger's Arch.. 125, 474 (1908). 



" Schroeder, "Die Hypothesen u. die Chcmische Vorgange bei der Kohlensaure- 

 Assimilation," Jena, 1917, p. 116, 



