j 
NOVEMBER 23, 1916] 
NATURE 
229 
I said nothing on the subject of compulsory Greek, 
but as my silence has been taken to imply complete 
assent to its abolition, let me say that while I have 
voted, and shall vote, against enforcing the study upon 
candidates for degrees in mathematics or natural 
science, I am convinced that the quality of any 
literary, historical, or philosophical study, whether in 
modern or ancient fields, is gravely injured wherever 
it is undertaken without a knowledge of Greek. 
Manchester, November 20. R..S. Conway. 
The Preservation of Natural Colour in Plants. 
In Nature of November 9 Dr. Rendle directs atten- 
tion to a method of producing compounds of chloro- 
phyll and copper similar in colour to that of the natural 
pigments of the leaf and of a comparatively stable 
nature. It may be worth while to point out that the 
chemical changes underlying the method are fairly well 
known, as a result of Willstatter’s investigations of 
chlorophyll and its derivatives. The knowledge derived 
from Willstatter’s work forms a very profitable basis 
for an investigation of the problem of preserving the 
colour of herbarium specimens. 
The chromogen complex of chlorophyll contains mag- 
nesium bound to nitrogen in a complex way. The 
chromogen group of chlorophyll a may be represented 
by the formula, C,.H,,ON,Mg. ‘The magnesium is 
easily removed by the action of acids, and the deriva- 
tives thus obtained, phzophytin, phytochlorin, etc., 
containing the group C,.H,.ON,, have optical proper- 
ties different from those of chlorophyll; in solutions 
they are of a yellowish-olive green colour, and they 
exhibit characteristic absorption spectra. 
It is possible in many cases to introduce a metal 
into these magnesium-free derivatives whereby com- 
pounds with optical properties similar to those of 
chlorophyll are produced. <A full discussion of the 
various methods for introducing the different metals is 
out of place here, but it may be pointed out that mag- 
nesium can be reintroduced into the chlorophyll mole- 
cule by treatment with methyl magnesium iodide. Some 
metals are very easily introduced—e.g. copper, zinc, 
and iron—by treating the magnesium-free derivative 
with the metallic acetates in acetic acid or alcohol; 
zine acetate even acts in cold solution. 
It is a remarkable fact that some of these metal 
compounds are more stable—for example, in relation 
to acids—than the original magnesium complex. It is 
possible to arrange the metals in a series according 
to the stability of the compound; the extremes of this 
series are potassium (very unstable) and copper (very 
stable). agnesium occupies an intermediate position. 
The procedure in the treatment of a specimen is thus 
the following :— 
(1) The Magnesium is removed from the Chloro- 
phyll.—This can easily be done in the case of plants 
with an acid cell-sap (e.g. Oxalis acetosella) by dipping 
them into boiling water. In other cases the tissues 
can be made permeable by treatment with alcohol or 
acetone (in “such a concentration that chlorophyll is 
insoluble, i.e. 10-60 per cent.). Subsequent treatment 
with dilute acid removes the magnesium. 
(2) The Metal is introduced.—It must be remem- 
bered that zinc, although a little less stable than 
copper, can be introduced without heating, and thus 
without the risk of injuring the specimen. The shade 
of colour obtained varies with the different metals. 
Investigations on these two points will no doubt 
add to our knowledge of the most suitable methods 
of preserving the colours of museum specimens of 
plants. INGVAR_ JORGENSEN. 
Department of Plant Physiology and Pathology, 
Imperial College of Science and Technology, 
London, November 14. 
NO. 2456, VoL. 98] 
Artillery and Rainfall. 
Tue following quotation may help to settle the ques- 
tion as to the effect of artillery on the rainfall, at any 
rate so far as the present generation of your readers 
is concerned. 
It is taken from a translation of ‘ Plutarch’s Lives,” 
by John and William Langhorne, and occurs in the 
life of “‘Caius Marius,’ where Plutarch comments on 
a battle fought against the ‘‘Teutones”’ in 102 B.c. 
“Tt is observed, indeed, that extraordinary rains 
generally fall after great battles; whether it be that 
seme deity chooses to wash and purify the earth with 
water from above, or whether the blood and corruption, 
by the moist and heavy vapours they emit, thicken the 
air, which is liable to be altered by the smallest 
cause.” 
Now, since the battles and rainfall referred to 
occurred some 1500 years before artillery was invented, 
it is clear that artillery cannot be the cause of the 
rainfall. Moriturvs. 
GOVERNMENT CONTROL OF FOOD 
SUPPLIES. 
1 eae oe difference of opinion may exist 
in regard to the stimulus which has moved 
the Government to take control of our food 
supplies, all are agreed that it has not come about - 
a moment too soon, and most will admit that we 
should now be much better off had it been taken 
in hand more than a year ago. 
The provisions outlined will empower the Food 
Controller to take measures both preventive and 
regulatory; the former to prevent waste, the im- 
proper use of food, such as giving to animals 
food that ought to be reserved for human beings, 
and market manipulation, cornering, or holding 
up of food supplies. The regulatory measures 
apply to the production ot flour from grain, the 
sale and distribution of articles of food, and the 
fixation of prices. 
If properly and intelligently applied, the scheme 
ought to work well. There can be no doubt that 
a great deal of food is still wasted, not alone by 
sections of the population who are earning more 
money than they have ever handled before, but 
also by public institutions; and many still believe 
in the catering for the Army, although this last 
has been improved. Nothing short, however, of 
some measure equivalent to “food tickets ” will 
prevent over-consumption and waste on the part 
of those who, owing to the war, are better off 
than in normal times. But by a strict system of 
inspection it ought to be possible to reduce or 
abolish waste in public institutions and in the 
Services. 
It is, perhaps, in respect to the application of 
the regulatory provisions that the public may 
harbour some misgivings, and particularly in 
respect to the manufacture of wheat-flour—a sub- 
ject which is dealt with elsewhere in this issue. 
The control of sale and distribution is certain 
to prove a difficult undertaking, but with suitable 
organisation it can in time be satisfactorily at- 
tained. The most delicate problem of all is, how- 
ever, the fixation of prices, and here expert know- 
ledge of food values will be indispensable if 
approximately the same amount of nourishment 
