502 
NATURE 
; [APRIL 14, 1923 

bore their part in the proceedings, singing, and playing 
on flutes and stringed instruments. 
The following and concluding article will deal with 
the monotheistic Aton-religion instituted by Okhnatén, 
and so enthusiastically practised and propagated by 
him at his capital, El-Amarna, in Middle Egypt. 
BIBLIOGRAPHY. 
J. H. Breasted, ‘‘ Development of Religion and Thought in Ancient 
Egypt,”’ London, r9r2. 
‘A. M. Blackman, “ The House of the Morning” (Journal of Egyptian 
Archeology, vol. V. pp. 148-165). 
By the same author also: 
“Some Notes on the Ancient Egyptian Practice of Washing the Dead” 
(Journal of Egyptian Archeology, vol. ii. pp. 117-123). 
“The eas of Women in the Ancient Revo Hierarchy ”’ (op. cit. voi. 
vii. pp. 8-30 
“The Sequence of the Episodes in the Egyptian Daily Temple Liturgy ” 
(Journal of the Manchester Egyptian and Oriental Society, 1918-1919). 
“Sacramental Ideas and Usages in Ancient Egypt. I. Lustra 
the Heliopolitan Sun-God ”’ (Proceedings of the Society of Biblical Archeology, 
vol. xl. pp. 57-66, 86-91). 
“* Sacramental "Ideas and Usages in Ancient Egypt. II. Osirian Lustra~ 
tions” (Recueil de travaux relatifs a la fhilologie et Varchéologie égyptiennes et 
assyriennes, Vol. 39, PP. 44-77)- 
The articles, “Priest and Priesthood’? (Egyptian), ‘ Purification” 
(Egyptian), “ Righteousness "’ (Egyptian), ee (Egyptian), in 
Hastings’s “‘ Encyclopedia of Religion and Ethics. 
The Photosynthesis of Plant Products.* 
By Prof. I. M. HEILBRoN. 
ESPITE the enormous strides that have been 
made by chemists during the last decades in 
the elucidation of many classes of plant products and 
the actual synthesis of individual members, the methods 
hitherto employed in the laboratory are so essentially 
different from those carried out by the plant that the 
synthetic processes of the living organism have come 
almost to be regarded as something fundamentally 
apart from those of the laboratory. The investigations 
on photosynthesis now being carried out in Liverpool by 
Prof. Baly and myself, although as yet of a quite pre- 
liminary nature, have, in my opinion, already shown 
that such a conclusion is entirely unwarranted and that 
the key to the problem of plant ‘syntheses i is to be found 
in the study of the energy transformations involved in 
the primary reaction wherein the plant brings about the 
fixation of atmospheric carbon dioxide. Apart from the 
purely academic interest of the subject, the problem of 
photosynthesis demands the attention of the community 
as a whole, for, with the elucidation of the reactions in- 
volved, the economic aspect of the question must inevit- 
ably become more prominent, and practical results of the 
greatest value to mankind may conceivably accrue. 
The work of the earlier investigators on the subject 
has led to the formulation of certain definite conclusions. 
Thus, it has been proved beyond question that photo- 
synthesis takes place in the green leaf of the plant and 
that, under natural conditions, assimilation apparently 
consists in the absorption of carbon dioxide by means 
of the chlorophyll contained in the chloroplasts and its 
deoxidation and condensation therein, in the presence 
of water and sunlight, to sugars. It is obvious that, 
in order to obtain any satisfactory explanation of the 
réle played by the chlorophyll, its constitution, and 
above all its reactions, must be known. The first 
advance in this direction is due to von Baeyer,? who 
suggested that the initial product of assimilation was 
formaldehyde, which then further condensed to form 
carbohydrates. This hypothesis was rapidly put to the 
test in two directions. Innumerable attempts have 
been made to prove the presence of formaldehyde in the 
_ green leaf itself, but in every case where this appeared 
to be established its formation could as readily be 
explained as being derived from sources other than 
assimilation. As regards the production of formalde- 
hyde from carbon dioxide in vitro, this has actually 
been carried out in numerous ways,? none of which, 
2 eps ance of lectures delivered at the Royal Institution on February 
r and 8, 
2 Ber. (1870) 3, 68. 
3 Usher and Priestley, Proc. Roy. Soc. (1906) B, 77, 369. 
NO. 2789, VOL. 111] 
however, are directly comparable with the conditions 
existing in the plant itself. The most detailed work in 
this connexion is that of Moore and Webster,* who 
showed that, under the action of light, formaldehyde 
was readily produced in solutions of carbonic acid con- 
taining colloidal uranium hydroxide or ferric hydroxide. 
As a result of these experiments, Moore concluded that, 
although chlorophyll had come to be universally re- 
garded as the fundamental agent for photosynthesis, 
the evidence was purely inferential, and it was more 
probable that the synthesis of formaldehyde in the | 
presence of sunlight was actually due to the inorganic 
iron present in the colourless portion of the chloroplast. 
Recent research shows this hypothesis to be i incorrect. 
Iron is undoubtedly essential to plant life, just as it is 
to animal life, and its function seems to be closely — 
associated with chlorophyll formation. Leaves starved 
of iron suffer from chlorosis but, in these, photosynthesis 
does not take place, and there can be little doubt that 
the real catalyst for the assimilation reaction is chloro- — 
phyll. Our knowledge of the constitution of this 
interesting and highly complex pigment is mainly due 
to the work of Willstatter and his collaborators,® who 
have established the fact that the following four pig- 
ments are invariably present in the green leaves of all 
land plants: Chlorophyll A, C;;H,,0;N4Mg, chloro- 
phyll B, C,;H,OgN4Mg, carotin, CyoHs,, and xantho- 
phyll, Cait O,. From an exhaustive study of the 
assimilation of carbon dioxide by the green leaf, 
Willstatter ® has been able to arrive at certain very 
important generalisations. He has found that in all 
cases the oxygen evolved is absolutely equivalent — 
to the carbon dioxide absorbed, which definitely 
proves that formaldehyde must be the first product, 
since the primary formation of such other substances 
as have from time to time been suggested would neces- 
sitate a volume ratio greater than r:1. Further, from 
the results of experiments carried out both in the leaf 
and in vitro, he has been able to show that, although 
chlorophyll is inactive to dry carbon dioxide, it is” 
nevertheless capable of combining with carbonic acid 
to form a labile addition compound. He concludes 
that this latter, by the absorption of light energy, - 
is rearranged into a formaldehyde peroxide complex 
from which, by means of enzyme action, formalde- — 
hyde is liberated, oxygen evolved, and chlorophyll 
regenerated. 
* Proc. Roy. Soc. (x913) B, 87, 163. 
5 Willstatter und Stoll, * «Untersuchungen liber Chlorophyll,” Berlin, 1913. 
. Willstatter und Stoll, “Untersuchungen iiber die Assimilation der 
Koblensiure,” Berlin, 1919. 

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