584 
and forming a hexavalent phenol which subsequently undergoes 
a molecular rearrangement and becomes glucose. 
Yet another suggestion was made by Bach in 1893. He 
points out that when sulphurous acid is exposed to light it 
becomes transformed to sulphuric acid, sulphur and water being 
split off, and he argues that a process analogous with this may 
take place in a leaf. The carbon dioxide uniting with water 
would form carbonic acid, and this might then split up in the 
same way as the sulphurous acid. The carbon and the water 
thus split off are on this hypothesis not set free separately, but 
in combination as formaldehyde. The higher carbon acid, to 
which Bach ascribes the formula H,CO,, splits up into carbon 
dioxide and hydrogen peroxide, and the latter is decomposed into 
water and free oxygen. 
Lieben has still more recently put forward the view that 
formic acid and not formaldehyde is formed by the first decom- 
positions. Tle has found that leaves of grasses and various 
trees yield formic acid among other products when mixed with 
their own weight of water containing a trace of sulphuric acid 
and distilled with steam. Moreover, when carbon dioxide is 
acted upon by nascent hydrogen the only product is formic 
acid. 
These speculations afford many points which might be well 
made the starting places of research. The views of Baeyer 
have met with most acceptance, though but little success has at- 
tended the few efforts that have been made to establish them by 
experiment. 
They involve several definite stages of action, of which the 
most important seem the production of carbon monoxide and 
hydrogen, the formation of formaldehyde and the construction 
of a sugar. The last two questions arise also in connection with 
the hypothesis of Bach. 
If we examine the work that has been published bearing on 
the probability of the formation of carbon monoxide in the 
plant we find little that is satisfactory. The statements that 
have been made are opposed to the idea that carbon monoxide 
is of value in nutrition ; it is said that when supplied to a plant 
instead of carbon dioxide it does not lead to the formation of 
carbohydrates. It is further advanced that this gas is of a very 
deleterious nature, and if formed would result in the speedy 
death of the protoplasm of the cell in which it originates. This 
idea is, of course, specious ; but it does not appear to be well 
founded. The deadly character of carbon monoxide when in- 
haled by a human being depends upon a peculiar interference 
which it causes with the oxygen-carrying power of the red 
blood corpuscles. The pigment hemoglobin to which these 
little bodies owe their usefulness forms a loose chemical com- 
bination with oxygen, the compound being formed in the blood 
vessels of the lungs and being decomposed with the liberation 
of the oxygen in those of the tissues of the body. It is evident, 
therefore, that the value of the corpuscles as oxygen-carriers 
depends upon their heemoglobin. When this pigment is exposed 
to carbon monoxide it combines with it in the same way as it 
does with oxygen, forming, however, a more stable compound. 
The affinity for this gas which the pigment manifests is very 
considerable. Hence the poisonous nature of carbon monoxide. 
It is easily seen that the latter is a poison because it throws out 
of gear and temporarily paralyses a most essential part of the 
mechanism of respiration, effectually preventing oxygen from 
reaching the tissues of the body. There is no evidence here 
that it exerts even a deleterious influence upon the living sub- 
stance itself. The only poisonous effect it would be able to 
exert on the plant would necessarily be of the latter character, 
for there is no oxygen-carrying mechanism that could be inter- 
fered with. We cannot lay any stress, therefore, on the ob- 
jection to Baeyer’s view, based upon the action of carbon mon- 
oxide upon the human organism. 
Another possibility may, however, be mentioned. As we 
shall see later, there are certain resemblances between hzemo- 
globin and chlorophyll, the vegetable pigment concerned in 
photosynthesis. May not carbon monoxide enter into some 
relationship with the latter, and thereby indirectly hinder its 
activity ? Of that, however, there is no trustworthy evidence, the 
facts known to us rather pointing in the opposite direction. 
The idea of the poisonous nature of this gas may easily be 
subjected to experimental examination. It would appear easy 
to expose a plant to an artificial atmosphere made up to different 
partial pressures of carbon monoxide, to expose it in such atmo- 
spheres to various conditions of warmth and illumination and 
to note the effect produced. It would seem possible to examine 
NO. 1719, VOL. 66] 
NATURE 
[OcToBER 9, 1902 
a great variety of plants in that way, to try both aérial and 
aquatic forms, and indeed to test the matter exhaustively. It 
must be borne in mind, however, that the solubility of carbon 
monoxide in water is extremely small, and that there may be a 
great difficulty in getting it brought within the scope of the in- 
fluence of the living substance on that account. It must neces- 
sarily be in solution in the cell sap before it can affect the 
activity of the chloroplast. Even the relations of solubility are 
not, however, outside the range of experiment, and it may be 
that the slightly acid celi sap has not the same peculiarities as 
water as a solvent for the gas. 
It is important, again, to take into account in such work the 
factor of sunlight, on which the power of photosynthesis de- 
pends. Should carbon monoxide prove capable of serving as a 
-basis for the formation of carbohydrates, the question would 
arise, Is the activity of the chlorophyll in sunlight confined to 
the preliminary formation of carbon monoxide from the dioxide, 
or is the energy derived from the light brought to bear upon the 
subsequent constructive processes? We have little or no accu- 
rate information as to the way in which the energy is utilised 
after absorption by the chlorophyll. 
This opens up a very important but very difficult line of work, 
which brings home to us the intimate dependence of vegetable 
physiology upon physics. The absorption of energy from with- 
out, in the form of the radiant energy of the solar rays, is cer- 
tainly a fact, and to a certain extent we can picture to ourselves 
the way in which it is secured. The spectrum of chlorophyll 
shows us a number of absorption bands whose position corre- 
sponds with the position in the spectrum of the places where 
oxygen is liberated in photosynthesis. But the transformation 
and applications of energy in the body of the vegetable organism 
need much closer examination. The intimate relationship 
between the different manifestations or forms of energy and the 
ways in which they can be transformed into one another have 
been very minutely scrutinised in recent times. What then 
should hinder us from learning something much more definite 
than we at present know about these transformations in the 
vile of vegetable life? The electrical phenomena connected 
with the movements of the leaves of the Venus’s fly-trap 
(Dionaea muscipula) have been examined with considerable 
completeness by Burdon Sanderson, and we have learned that 
the vegetable and animal organisms show considerable similari- 
ties in this respect. Recently, again, Bose has made important 
contributions to the subject of the electrical responses to stimu- 
lation that can be observed under particular conditions. A 
promising beginning has thus been made, but only a beginning. 
The electrical condition of the normal plant under different 
conditions of rest and activity has still to be investigated. If 
we return to the subject of photosynthesis and the work done by 
the chloroplast, may we not hope to discover something about 
the transformation and utilisation of the radiant energy asso- 
ciated somehow with this structure? Considering the relations 
between the manifestations of energy which we appreciate 
respectively as light and electricity, it does not seem wildly im- 
probable to imagine that the energy absorbed as the former may 
lead to a possible electrolysis of carbonic acid under the influ- 
ence of the chloroplast, with the formation of carbon monoxide 
and oxygen. Pfeffer has suggested that perhaps the decom- 
position of the gas is not due to the light rays at all, and that 
they may exercise only a stimulating influence upon the chloro- 
plast, the energy concerned being derived from heat rays directly 
absorbed, or heat vibrations derived from the more rapidly 
vibrating light rays. In this case is the decomposition brought 
about directly by the heat vibrations, or have we a transmutation 
into some other form of energy? The whole subject seems at 
all events a promising subject for inquiry. 
Another problem connected with the action of chlorophyll 
is associated with the absorption of radiant energy by the 
different regions of the spectrum. Bands of considerable inten- 
sity are noticeable in the blue and violet, though the deepest 
absorption takes place in the red. Yet Engelmann’s classic 
bacterium method shows us that very little evolution of oxygen 
takes place in the position of these bands in the blue and violet. 
The fact that absorption of radiant energy and photosynthetic 
activity show no quantitative relationship is of course not new, 
but the reason remains still to be discovered. Van Tieghem 
has suggested an explanation which recalls to us the hypothesis 
advanced by Pfeffer, just alluded to. This explanation is that 
there are two factors concerned in the action of chlorophyll, the 
elective absorption of light, shown by the occurrence of the 
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