438 Baker . — Quantitative Experiments on 
these two accounts would alter the proportion obtaining between the loss in 
dry weight of the plant and the amount of carbon dioxide evolved. 
This result is the reverse of that obtained from a consideration of the 
former results (with aniline as absorbent for formaldehyde, see p. 435), 
which were comparative but not strictly quantitative. This illustrates the 
great danger in drawing definite conclusions from purely comparative data. 
Theoretical Deductions from Results. 
This leads to the conclusion that formaldehyde, as it can be assimilated 
to some extent by plants in light (p. 422), is probably a step in photo- 
synthesis, but that the further steps in this process also require light 
energy. In this case, the next step after formaldehyde must be a substance 
still more unstable than formaldehyde itself. Recent work on this subject, 
e. g. Usher and Priestley’s 1 investigations on the extra-cellular production 
of formaldehyde from carbon dioxide in light, as well as the theories of 
Baeyer, Erlenmeyer, and Bach, are only concerned with the first step in 
photosynthesis, the assumption being that the subsequent processes — carried 
out, according to Usher and Priestley’s work, 1 by the protoplasm — consist 
merely in the polymerization of formaldehyde. The electrical theory of 
photosynthesis, announced by J. Harvey Gibson, 2 also only accounts for 
the production of formaldehyde from carbon dioxide. The experiments 
which have been described seem to indicate that, if formaldehyde is part of 
the natural scheme of photosynthesis, the subsequent processes are much 
more complex than has often been supposed. It should, however, be 
noticed that such an authority as Meldola 3 seems to lean to the less simple 
explanations of the phenomenon. 
Various suggestions have been brought forward at different times as to 
the nature of the substances formed from formaldehyde in photosynthesis. 
Fischer 4 suggested glycerose, and Piloty 5 glyceric aldehyde with dihydroxy- 
acetone, as steps in building up the hexose molecule. These substances 
have not been found in plants, nor would the processes require light energy. 
In my opinion the most plausible suggestion is that due to Collie, 6 that 
keten, or some similar compound, is the first step in the process, after the 
production of formaldehyde. This substance keten, whose formula is CH 2 , 
CO 
is the first member of the extraordinarily reactive series of compounds, of 
the same general formula, known as polyketides. From substances of this 
1 Usher and Priestly : Proc. Roy. Soc., lxxxiv, B. p. 101. 
2 Gibson : Ann. of Bot., 1908, xxii, p. 117. 
8 Meldola : Trans. Chem. Soc., lxxxix, p. 749 et seq. 
4 Fischer: Ber. d. Deutsch. Chem. Ges., 1890, xxiii, 2138. 
6 Piloty: Ber. d. Deutsch. Chem. Ges., xxx, 3166. 
6 Collie: Trans. Chem. Soc., 1907, xci, 1806. 
