268 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
[ April 2, 1835. 
ought to be done. A winter never passes now without one or more pro¬ 
longed spells of fog, contaminated with the jn’oducts of coal combus¬ 
tion. For weeks at a time, during the winter, the London suburbs are 
enshrouded in semi-darkness whilst the air is tainted with foreign and 
offensive matter. Coincidently, there occurs a dropping of buds, a 
destruction of flowers, and, what is more serious, a wholesale annihila¬ 
tion of the foliage of most tender, softwoodcd stove plants. The leaves 
of certain genera of Orchids and of hardwooded plants turn yellow when 
these visitations are prolonged. It seemed to the Scientific Committee 
desirable that steps should be taken to ascertain to what constituents of 
fogs the various classes of injury, enumerated above, are due ; ■what part 
is played by the various acids present ; whether the tarry products exert 
any specific action ; and how far the conditions of semi-darkness partici¬ 
pate in the destruction. It was also considered desirable to make special 
investigation into the exact nature and amount of the impurities present 
in urban fog, and to observe the varying effects on vegetation of fogs 
differing in quality. The Committee, though hardly sanguine that any 
knowledge that might be obtained by such an investigation would lead 
to any effective abolition of the evil, was of opinion that such an inquiry 
was desirable in view of the great interest of the question. In any case, 
such knowledge was necessary before special cultural precautions could 
be recommended as likely to mitigate the evil to an appreciable extent. 
A full understanding of the disease must precede any steps for its 
amelioration. Whilst the Scientific Committee was arranging for the 
carrying out of a systematic inquiry in the London area, the Manchester 
Field Naturalists’ Society was taking steps in a similar direction. The 
Manchester Committee proposed to make systematic analyses of fogs at 
many stations and at various elevat'ons, with a view to finding out 
everything appertaining to the genesis and composition of their city 
fogs, with especial reference to their injurious effects on animal and 
vegetable organisms. Further reference will be found in the body of 
this report to the Manchester investigation. 
Since October last, the London inquiry has been in active operation. 
Circumstances have led the Committee to look to me for the execution 
of this research hitherto, and I now summarise shortly the general 
lines along which the inquiry has proceeded. Throughout I have had 
the constant advice and help of my colleagues on the Committee, and 
my task, without their many suggestions, would have been a more difficult 
one than it has actually been. It is not proposed to enter here into the 
accumulations of facts bearing on the question that I have been able to 
collect by observation, correspondence, and experiment, but to indicate 
only the lines of inquiry in the hope of obtaining criticisms likely to be 
of value in the further prosecution of the work. It will not be p'ossible 
or desirable to prepare any detailed report till another year has elapsed. 
My observations so far deal almost entirely with plants cultivate 1 under 
glass. It will be convenient for the purposes of this report to take the 
several lines of inquiryq and to deal with them in successive paragraphs. 
I. L I'han Fog and Countrg J/ist .—In an inquiry into the action of 
so complex a product as urban fog it was of the greatest importance to 
obtain reliable data as to the effect on vegetation, if any, of pure country 
mists, uncontaminated by smoke. It was impossible for me personally 
to make the observations needful to establish the injurious or other 
action of mist upon plants ; but, by the courtesy of correspondents in 
country districts, quite away from areas of smoke genesis, it would 
appear, so far as observations are as yet to hand, that little or no injury 
to stove or emservatory plants arises from this cause. Indeed, pure 
mists would seem to be beneficial to certain classes of cultivated plants. 
In those instances in which any injury obtained it was, in most cases, 
referable to some other cause. The establishing of this point is of great 
importance, since foggy weather is so frequently attendant upon spells 
of frost, and it has been frequently suggested that the increased stove 
heat needful to maintain the requisite temperature would have a harmful 
action. Indeed, I was quite prepared to find this to be the case at the 
outset of the inquiry. My own observations during cold weather in 
London without fog, and the evidence to hand from a distance as to 
frost with and without mists, point to the fact that, with proper pre¬ 
cautions, no appreciable damage is done to plants. 
In general, the same remarks apply to small towns away from 
manirfacturing areas. With the increase in the .size of the towns, the 
conditions more nearly approximate to those of London. The fog 
leaves the well-known deposit of filth on glass houses and evergreen 
foliage ; and if such districts escape the more serious effects observable 
in or near the larger smoke-producing areas, it is due to the relatively 
small concentration of the impurities in those fogs. It seems to me 
desirable to obtain accurate analyses of fogs from some country town of 
say 50.000 inhabitants, in which manufactures are not carried on, for 
comparison with similar analyses from the metropolis. 
II. Fo'tent of the London Fog Area .—I have been at great pains 
to ascertain how far the London fog cloud extends around the metro¬ 
polis. In this I have had the most cordial co-operation of our nursery¬ 
men and cultivators, who have supplied me with detailed information 
as to the times of occurrence of fogs, and as to the nature and extent 
of the injuries sustained. In many cases I have availed myself of the 
opportunity to visit their collections, and form an estimate of the 
damage done, valuable for purposes of comparison. The extent of the 
fogs is greatest in a westerly and south-westerly direction, and has been 
traced as far as thirty-five miles away westward, and twenty-five miles 
south-west, under special atmospheric conditions. Exceptionally the 
London fogs are met with at even fifty miles distance on this side. 
With the wind in an easterly or north-easterly direction these outlying 
districts receive visitations of fog with the accompaniments of sooty 
deposits and sulphurous smell. No doubt the concentration is not so- 
considerable nor the duration so long as nearer London, but it^ is 
sufficient to at once affect the buds and flowers of such sensitive- 
Orchids as Laelia anceps, Cattleya Trianre, Calanthe, &c. The effect of 
the fog on foliage at these distances is fortunately small, though in 
certain instances it is sufficient to destroy the seedlings of Cucurbitas,. 
Tomatoes, &c., which are extremely sensitive. As one follows the effects 
of fog down the Thames valley, from the most outlying .stations affected, 
to London, the observed effects increase in severity, till they are indis¬ 
tinguishable from those noted at stations actually within the metropolis. 
At Kew, for instance, the destruction has been most disheartening, it 
having come to flowers, flower buds, and foliage alike. Effects or 
similar nature, but less in total magnitude, are reported from spots five 
miles further west. Southwards, the North Downs afford a valuable 
barrier, which in many cases ■would seem to filter off the more deleteri¬ 
ous constituents of the fog. Indeed, the configuration of the country 
and the nature of the subsoil have an important influence in determin¬ 
ing the immunity of a given locality from damage. Eastwards I have 
information as to damage from so great a distance as Maidstone, over- 
thirty miles. All my correspondents emphasise the non-hurtful nature 
of the sea fogs prevalent in this quarter. To the north and north-east 
the fogs effects do not extend to such extreme distances, and the con¬ 
ditions for winter cultivation are consequently more favourable for 
cultivation on that side of the metropolis. Mr. E. Mawley of Berk- 
hampstead has furnished me with some interesting meteorological 
details regarding fogs extending to this locality (twenty-six miles- 
N.W.). . 
The tabulation of the information bearing on the srrbject of this 
paragraph will form a valuable appendix to my detailed report. 
III. The Fogs of the Winter 1890 91 .—It is needless to say that the 
past winter has been one singularly favourable for the purposes of an 
investigation of this character. The season opened with a severe fog of 
short duration during the second week of October, which left its traces 
on vegetation in the London area. This was the only serious instance 
of a fog on which observations of hardy plants could be made, as the 
conditions were not complicated by the presence of frost. I am indebted 
to C. T. Druery for an interesting account of its effects, unprecedented 
in his experience, upon his collection of hardy Ferns at Forest Gate. 
Though there were minor fogs during November it was during the long 
periods before and after Christmas, and again in February, that all the 
worst effects were exhibited by vegetation under glass. These two 
spells differed considerably in their nature. The Christmas fogs were 
accompanied by exeeptionally severe frosts, were on the whole much 
darker overhead, and contained a larger amount of noxious matter. In 
addition to this the duration of daylight was considerably shorter than 
in February. On the other hand, though in February the fogs were 
exceedingly opaque, the general average of light reduction was not so 
gre.at as at Christmas. The vertical extent of the fogs in February was 
such that on many occasions the sun was able to partially disperse them, 
for a short period at noon. 
Both fogs had a marked effect on flowers, but on the whole at 
Christmas, to instance only one genus of plants, Cypripedium, the effects 
were much more markei. Cypripedium is perhaps as little affected by 
fogs as any genus of Orchids I have met with. Yet, in a large collection,, 
continuously under my observation, it was patent that the damage done 
was markedly less in February than at Christmas. In the collections or 
plants under observation the damage to foliage was also greater during 
the former; this both as regards the dropping of leaves, which I have 
reason to believe to be greatly brought about by the recluction of light 
for a lengthened period, and also in the formation of actual corrosions of 
portions of the leaf surface. 
It must be remembered, in estimating the relative damage caused by“ 
these two fogs, that the earlier one distroyed a greater part of the- 
foliage of very mrny soft wooded plants, so that there was less surface 
exposed for attack at the second occasion. Nevertheless, so favourable 
were the circumstances during the latter part of January and the first 
week in February, that rapid growth had in many cases taken place. 
If we narrow the comparison to the damage (corrosions) sustained by 
young, and relatively unprotected leaves during the two periods, without 
doubt that at Christmas was immeasurably greater than in February- 
These remarks are based on observations on collections continuously 
under my eye, and situate in the worst districts. Full details are not 
yet to hand from correspondents at orrtlying stations, so that it is 
possible I may have to modify these observations when I come to take a 
general survey. Thus at Kew, the ill effects noted after the February 
fogs were quite as bad as at Christmas, whilst further east the reverse 
was the case. Other considerations confirm the view, that in February 
the fog-nucleus was several miles further west than at Christmas. I 
have in my notes full details of the damage obtaining from these fogs 
from many sources, but with these horticulturists are, in general, only 
too familiar, and they may well be reserved for the report on the whole 
question. 
IV. Constitution of Fog .—On a purely chemical question, such as 
that of the constitution of fog, I am scarcely entitled to speak. How¬ 
ever, since at the outset of this inquiry it W’as deemed advisable to obtain 
as much information on the matter as possible, with especial reference 
to those components deleterious to vegetation, I will state briefly what 
has been done. 
The Meteorological Council very readily put at our disposal the pump 
and apparatus originally constracted for Dr. W. J. Eussell’s investigation. 
The whole apparatus was thoroughly revised and set up under the 
