APRIL 14, 1923] 






































This work still leaves much unexplained and in no 
way helps to disentangle the paradox that whereas, on 
one hand, formaldehyde must actually be produced, 
it nevertheless does not exist in the leaf. Nor does it 
afford an explanation of the rapid synthesis of either 
the disaccharides, such as cane-sugar, or of storage 
‘starch. Again, it is curious that, if the reactions are 
actually those specified by Willstatter, Nature should, 
apparently by caprice, invariably ensure the presence of 
the two chlorophyll components and also the carotinoid 
igments, when one chlorophyll individual would by 
itself be sufficient. It would seem more probable that 
the four pigments are present because each has an 
absolutely definite réle to play in the mechanism of 
assimilation. This suggestion is strongly supported by 
a consideration of the striking oxygen values existing 
between the two pigment classes, these being in strict 
agreement with the amount of oxygen liberated in the 
photosynthetic operation. 
Returning now to the consideration of the primary 
synthesis wherein carbonic acid is deoxidised to formal- 
dehyde, this reaction is a highly endothermic one, 
impossible to realise under the conditions commonly 
employed in the laboratory. On the other hand, car- 
bonic acid is able to absorb light of very short wave- 
length (A=200 pp), and, if exposed to light of this 
frequency, the formation of formaldehyde, without the 
agency of any catalyst, can readily be demonstrated 
under these purely photochemical conditions. More- 
over, in the presence of a suitable basic coloured 
substance, such as malachite green, with which the 
carbonic acid can combine loosely, the formation of 
formaldehyde can be demonstrated in visible light, the 
malachite green acting as a photocatalyst for the 
reaction.” 
Le 
CARBOHYDRATE PRODUCTION. 
The formation of sugars on exposure of aqueous 
solutions of formaldehyde to ultra-violet light was 
demonstrated by Moore and Webster.8 These observa- 
tions have been fully confirmed, and it has been found 
that the wave-length of light which brings about this 
Teaction (A=290 pp) is photochemically distinct from 
that required for the synthesis of formaldehyde itself. 
In our earlier experiments in Liverpool, it was con- 
sidered that the photosynthetic formation of carbo- 
hydrates had to take place in two distinct stages, but, 
as will be explained below, later experiments have 
shown that this interpretation was incorrect, the actual 
process being simpler. The formaldehyde molecule, 
when first produced by photosynthesis from carbon 
_ dioxide, exists in a highly reactive phase, identical with 
that obtained when ordinary formaldehyde is photo- 
_ chemically activated. This type of formaldehyde we 
have designated “activated formaldehyde,” and it is 
this which must be photocatalytically produced through 
the agency of the chlorophyll, and immediately 
condenses to sugars, for, as is well known, ordinary 
formaldehyde has no such property. It follows from 
this that the formaldehyde detected in the carbonic 
acid experiments cannot have been a direct product of 
photosynthesis, but must have resulted from a sub- 
sequent decomposition of photosynthesised sugar. 
That carbohydrates readily yield formaldehyde under 
? Baly, Heilbron, and Barker, Jour. Chem. Soc. (1921) 119, 1025. 
8 Proc. Roy. Soc. (1918) B, 90, 168. 
NO. 2789, VOL. 111] 
NATURE 
593 
the influence of short wave-length light has been proved 
experimentally, and thus the detection of formalde- 
hyde in any photochemical operation may be regarded 
as sure evidence of photosynthesis. 
The investigation into the nature of the sugars formed 
by the photochemical activation of formaldehyde is still 
being carried out, but we have been able to prove con- 
clusively that the condensation leads to the production 
of hexose sugars alone. This fact affords a ready 
explanation of the formation of disaccharides and 
starches, for the freshly photosynthesised hexose mole- 
cule must exist in a highly reactive phase, and con- 
sequently further condensations will inevitably take 
place. 
NITROGEN ASSIMILATION. 
The problem as to the origin of the many classes of 
nitrogen compounds occurring in the vegetable kingdom 
is one fully equal in importance to that of the formation 
of carbohydrates, but although many have speculated 
on their possible synthesis, little definite evidence has 
hitherto been adduced to account for their production. 
The questions which have to be considered in this con- 
nexion are, first, under what conditions and in what 
state does the nitrogen enter the plant, and secondly, 
is the fixation process a photosynthetic reaction ? 
With regard to the manner in which nitrogen is supplied, 
the general method would appear to be that it passes 
into the roots in the form of nitrates, or possibly 
ammonium salts, present in the soil. In addition to 
the introduction of nitrogen in this manner, Moore ® 
has found that in the case of unicellular alge, providing 
abundant carbon dioxide is present, elemental nitrogen 
from the atmosphere can be absorbed and directly 
utilised. This discovery, which is of quite exceptional 
interest and fully corroborates Jamieson’s ?° earlier 
investigations, is still further supported by the recent 
observation of Lipman and Taylor," who claim to have 
proved that ordinary wheat is able to assimilate up to 
20 per cent. of its total nitrogen content in the form of 
free nitrogen. 
It was noted by Schimper that nitrites are invariably 
present in the green leaf when kept in the-dark, but 
that they rapidly disappear on exposure to light, and 
the deduction may thus be drawn that these are the 
active substances employed in the nitrogen fixation. 
The direct assimilation of atmospheric nitrogen in no 
way invalidates this conclusion, for there can be little 
doubt that the free nitrogen will readily react with the 
nascent oxygen formed during the photolysis of the 
carbon dioxide to yield oxides of nitrogen. 
With these facts in mind, exhaustive experiments are 
now being carried out in Liverpool on the interaction of 
nitrates with activated formaldehyde. It has been 
found that under all conditions the primary reaction 
- HV 
product is formhydroxamic acid,’ y, C=NOH, a 
HO ; 
substance which had previously been obtained by 
Baudisch }¥ in his pioneer work in this field. The forma- 
tion of formhydroxamic acid takes place only in the pres- 
ence of activated formaldehyde, no trace of it being found 
® Moore and Webster, Proc, Roy. Soc. (1920) B, 91, 201 ; (1921) B, 92, 51. 
1° Reports Agricultural Research Association, Aberdeen (1905-1911). 
1 Science, 1922, November 24. 
42 Baly, Heilbron, and Hudson, Jour. Chem. Soc. (1922) 121, 1078. 
1 Ber. (1911) 44, 1009. 
