OcToBER 9, 1902] 
NATURE 
585 
absorption bands in the spectrum, and the calorific energy of | comparatively harmless modification. This will slowly decom- 
the absorbed radiations. The failure of the rays of the blue and 
violet to effect photosynthesis, in spite of their absorption, would | 
on this view be attributable to their possessing but little calorific 
energy. The latter is associated much more strongly with the 
deep band in the red, which is the seat of the maximum evolu- 
tion of oxygen when the spectrum is thrown upon a collection 
of active chloroplasts. The heating rays alone are ineffectual, 
as shown by the fact that there is no liberation of oxygen in the 
region of the infra-red, due no doubt to the fact that chlorophyll 
does not absorb these rays. 
Timiriazeff, in his classical researches on the liberation of 
oxygen by the leaves of the bamboo when exposed in tubes of 
small calibre to a large spectrum, found that the amount of 
carbon dioxide decomposed by leaves is proportional to the 
distribution of effective calorific energy in the spectrum. 
Van Tieghem’s hypothesis that this is a matter of calorific 
energy may prove to be erroneous, and yet his views may rest 
on some sound basis. It may be a matter in which electrical 
rather than caloiific energy may be concerned. 
Returning now to the chemical steps demanded by Baeyer’s 
hypothesis, there are certain considerations which may be urged 
in favour of the view that carbon monoxide really occurs in 
photosynthesis. It has been ascertained by Norman Collie that 
when a mixture of gases containing a large proportion of carbon 
dioxide is exposed at low pressures in a vacuum tube to the 
action of an electric discharge from an induction coil, there is a 
very large formation of the monoxide, together with oxygen, in 
some cases as much as 70 per cent. of the gas undergoing | 
decomposition. 
Appealing to the experience of various observers, there seems 
on the whole to be a balance of evidence in favour of the power 
of plants to live and prosper in an atmosphere containing a very 
considerable percentage of carbon monoxide. 
The question of the possibility of the latter replacing the 
dioxide, as the theory appears to require, is complicated very 
seriously by the differences of solubility between them. Carbon 
dioxide dissolves very readily in water and in cell sap ; carbon 
monoxide is almost insoluble in either. As the amount of a gas 
taken up by a solvent depends, not onlyon its solubility, but 
upon its partial pressure, it is very evident that we cannot 
compare the two gases by admitting the same quantity of both 
to plants under simultaneous comparison, It is only necessary 
to supply the dioxide in the proportion of four parts in 10,000 ; 
but the almost insoluble nature of the monoxide makes it 
inevitable that from 2 to 5 per cent. shall be experimented with. 
The same question of solubility makes it almost out of the 
question to experiment with an aquatic plant. 
It would be of considerable interest from this point of view 
also to inquire whether if carbon monoxide is liberated at the 
outset of the photosynthetic processes its combination with other 
groupings can take place apart from the action of chlorophyll. 
If so, the fungi should be capable of carbohydrate construction 
if supplied under proper conditions with the monoxide and with 
hydrogen. The proper conditions, however, might be extremely 
difficult to establish. 
The next stage in the constructive process affords still ample 
room for investigation. The presence of formaldehyde is not 
the hypothesis of Baeyer alone, but is demanded according to 
Bach’s views, though the stages of its hypothetical construction 
are not the same. We have therefore to ask whether form- 
aldehyde can be detected in plants, and if so whether the 
conditions under which it may exist admit of its being con- 
sidered an up-grade product in photosynthesis. Objections to 
the theory of its formation may be advanced, based upon its un- 
doubtedly poisonous nature. Ofall the antiseptics now avail- 
able to the bacteriologists it is perhaps the most potent, even 
traces being fatal to the form of vegetable protoplasm which is 
found in bacteria. We may argue that it must be equally dele- 
terious in the cell containing chlorophyll and to the chloroplast 
itself, as we have no reason to suppose that any difference in 
vitality exists between the protoplasm of different plants. At 
first sight this appears an almost insuperable difficulty in the 
way of the theory. Formaldehyde has, however, the properties 
of aldehydes in general, one of which is the power of condensa- 
tion or polymerisation. It passes with extreme readiness into a 
much more inert form, para-formaldehyde, a body in which 
three molecules of the formaldehyde are grouped together. It 
_ itself. 
is therefore possible that it may be prevented from exercising 
its deleterious properties by a transformation at once into this | 
NO. 1719, VOL. 66] 
pose under proper conditions, giving off the free aldehyde. 
Pollacci has stated that it is possible to extract formaldehyde 
from leaves. In his experiments he took such as had been ex- 
posed to light for a very considerable period and then macerated 
them in water. After a sufficient extraction he distilled the 
leaves, together with the water in which they had been steeped. 
The first portions of the distillate yielded reactions indicative of 
the presence of formaldehyde. His experiments do not enable 
us to say that free formaldehyde was there, for the more stable 
para-form would be likely to decompose during the distillation, 
so that the reactions would be explained without demanding 
the presence of the free aldehyde in the leaves. 
But little success has attended hitherto the attempt to show 
that formaldehyde, in the presence of chlorophyll, or preferably, 
| we may say, of chloroplasts, can give rise to carbohydrates. We 
have nothing more satisfactory than Bokorny’s experiments, in 
which, after failing to set up photosynthesis in a filament of 
Spirogyra fed with formaldehyde, he succeeded when he supplied 
the alga with its compound with sodium-hydrogen-sulphite. 
Experiments on a more comprehensive scale, conducted on a 
variety of plants of different habits, are needed before we can 
regard the process as satisfactorily established. 
We have further to pursue the problem by an inquiry as to the 
nature of the sugar first formed. Certain considerations lead to- 
the view that it is probable that a sugar of the aldose type must 
be accompanied in the plant by a ketose. The hypothesis as. 
stated by Baeyer, and so far accepted until quite recently, took 
no account of the latter. The aldose g7afe sugar was the one 
always suggested, and from this all others met with have been 
held to be constructed. The first appearance of a ketose, 
Jevulose, or fruzt sugar, has been associated with the hydrolytic 
decomposition of cave sugar, itself constructed presumably from 
the grape sugar. I fear sufficient attention has not been paid to 
probability or to the normal course of chemical action in framing 
our hypotheses, for it is rather difficult to see how some of the 
transformations somewhat dogmatically affirmed can_ possibly 
take place. I may refer in passing to the statement that in the 
digestion of fat or oil during germination part of it is converted 
into starch or sugar. 
But to return to the construction of sugar. The condensation 
of formaldehyde, which can be brought about by the action of 
basic lead carbenate, leads to the formation of several sugars, 
each yielding its characteristic osazone. How far the condensa- 
tion in the plant follows this is still uncertain. It is quite pos- 
sible that stages intervene between formaldehyde and sugar of 
any kind. It has been suggested that formaldehyde in the 
presence of water may under the conditions obtaining in the leaf 
| give rise to glycolaldehyde, a body which forms sugar very 
| readily indeed. 
| hyde is a much longer process and is attended with greater 
| difficulty. 
The formation of sugar directly from formalde- 
I may call your attention here to the views of Brown and 
Morris traversing the theory of the primary carbohydrate being 
grape sugar. In their classical paper on the chemistry and 
physiology of foliage leaves, they have adduced strong evidence, 
based upon analyses of the sugar-content of leaves of Zvepacolum 
majus, that in this plant at any rate the first sugar to be formed 
is cane sugar. Whether or no this is the case in plants generally 
cannot at present be said, though it appears from many con- 
siderations probable. 
The part played by chlorophyll in photosynthesis has already 
been touched upon. Remarkably little is known about chlorophyll 
It has so far been found impossible to extract it from the 
chloroplast without causing its decomposition, and hence our ideas 
of its constitution, such as they are, are based upon the examina- 
tion of something differing in some not well-ascertained parti- 
culars from the pigment itself. A remarkable relationship is 
known to exist between the latter and iron, for unless this metal 
is supplied to a plant its chloroplasts do not become green. But 
the condition of the iron in the plant is uncertain; it seems 
probable that it does not enter into the molecule of the pigment 
at all. A remarkable series of resemblances between deriva- 
tives of chlorophyll and derivatives of hematin, the colour- 
ing matter of haemoglobin, has been brought to light by the 
researches of Schunck and Marchlewski, which is very sugges- 
tive. The same leaning towards iron is found in the two 
pigments, but in the case of hematin our knowledge is further 
advanced than in that of chlorophyll. The iron is known to be 
part of its molecule. It can by appropriate treatment be 
