138 



SCIENCE 



[N. S. Vol. X\CXIII. No. 839 



which he concluded that formaldehyde is 

 undoubtedly present in the green parts of 

 living plants when exposed to sunlight. 

 He experimented directly with the grow- 

 ing plant, as well as with the liquid ob- 

 tained by distilling the leaves in a current 

 of steam. Twigs were bent down from the 

 growing plant into cylinders containing 

 Sehiff's reagent. It was found that when 

 the experiment was carried on in the sun- 

 light the red color gradually developed, 

 which resiilt was attributed by the investi- 

 gator to the production of formaldehyde. 

 While the results obtained by the tests 

 made directly upon the leaves were only 

 suggestive and not conclusive, the distillate 

 from the leaves Polacci affirms undoubt- 

 edly contains formaldehyde itself. Many 

 tests were employed. Some of these were 

 of a general character, while others were 

 definite for formaldehyde itself. Special 

 stress is placed on (a) the color test ob- 

 tained by successive additions of phenyl- 

 hydrazine, nitroprussiate of sodium and 

 alkali; (&) the color test with sulphuric 

 acid and codeine; (c) Trillat's color test 

 with an aqueous solution of dimethyl ani- 

 line in the presence of acetic acid and lead 

 peroxide; (d) the reaction with phenyl- 

 hydrazine; (e) the color test with phenol 

 and sulphuric acid. A short time after 

 the publication of the results of Polacci 's 

 experiments two other Italian investiga- 

 tors, namely Plancher and Ravennaj^^* 

 reported a series of similar experiments, 

 but failed to find any conclusive proof of 

 the presence of formaldehyde in plants. 

 The formation of color in Sehiff's solution 

 under the conditions of Polacci 's experi- 

 ment was attributed not to the presence of 

 formaldehyde, but to the "active" oxygen 

 evolved by the plant in the process of as- 

 similation. They likewise claimed that 

 the tests which Polacci employed for the 

 ^ Atti d. Real. Accad. d. Linoei, 13, p. 459. 



detection of formaldehyde in the distillate 

 from green leaves are untrustworthy. In 

 order to determine whether formaldehyde, 

 if present in the green leaves, would actu- 

 ally distill over or would remain combined 

 with compounds in the plants, these in- 

 vestigators added a very dilute solution of 

 formaldehyde to leaves before distillation 

 and then tested for formaldehyde in the 

 distillate. The results showed that the 

 amount of formaldehyde which must be 

 present in the leaves in order to respond to 

 conclusive tests in the distillate is so large 

 that it would destroy at once the vitality 

 of the plants. Polacci 's results have also 

 been criticized by Czapeck''* as being in- 

 definite. Euler,"^ on the other hand, con- 

 firms his results, although he expresses the 

 opinion that the formaldehyde is not pres- 

 ent in a free state in the plant, but is lib- 

 erated from its condensation products by 

 the process of distillation. In a more re- 

 cent article Polacci^" refers to the criti- 

 cisms of his investigations and defends his 

 original conclusions with great vigor. 



Among the other investigators may be 

 mentioned Grafe^' as well as Kimpfiin,'^ 

 both of whom maintain that formaldehyde 

 is undoubtedly present in the growing 

 plant. The former investigator used a 

 solution of diphenylamine in sulphuric 

 acid as a test, claiming that this reagent 

 gives a green coloration with exceedingly 

 minute quantities of the aldehyde. Kimp- 

 flin, on the other hand, recognizing that 

 formaldehyde, if present at all, can only be 

 present in minimal amounts, ingeniously 

 attempts to store up the compound as fast 

 as formed until a sufficient quantity is 

 obtained to respond to the tests. To do 



"Bot. Zeit., 1900, p. 153. 



"^Ber. d. chem. Gesell., "il , p. 3411. 

 ^ Atti d. Real. Accad. d. Linoei, 16, p. 199. 

 " Oesterreioh. lot. Zeitschrift, 1906, No. 0. 

 ^ Compt. rend., 144, p. 148. 



