288 
[ April 9 , 1801. 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
summers are greatly against success with these plants ; very seldom 
indeed do we see them in satisfactory condition. At Gouville, 
however, they are as strong and healthy as could be wished, and 
close attention to their requirements and to ensure freedom from 
insect pests is the only secret of the success. Various small houses 
are devoted to Caladium=>, Bertolonias, Anthuriums, and propagat¬ 
ing purposes, not the least important of which is the raising of 
seedling hybrid Orchids, of which numbers have been obtained, and 
from very interesting crosses. 
To the fruit garden, which comprises a large collection of 
trained trees, the vineries the Peach and Strawberry houses, some 
notes will be devoted on another occasion, when I hope to supple¬ 
ment them by some further observations on the fruit culture of 
Normandy. My thanks are due to the Comte de Germiny for the 
kindly reception he accorded me, and for the generous invitation 
to visit Gouville at a more favourable time of year. To his skilful 
gardener, M. Vincent, I am also indebted for courteous attention 
during an extremely pleasant though brief visit.— Lewis Castle. 
UNFORCED DWARF RHUBARB. 
I HAVE read with much interest (in the Journal of Horticulture, 
March 2(>th), a short paper on the earliness of Rhubarb, by my obliging 
correspondent, Mr. N. H. Pownall, of Lenton Hall Gardens, to whom, 
in August, 1889, I supplied five buds of my Yaxley Rhubarb, Avith 
cultural directions. I am glad to infer that the kind stands well in the 
opinion of so expert a Rhubarb grower, who has written, as I appre¬ 
hend, only of natural Rhubarb unforced in any way. 
Mr. Pownall states that this year he began to pull the Yaxley 
Rhubarb on 23rd Mareh, and gives the dimensions of the stems. Avhich 
for so young a plant prove a thoroughly skilful treatment. Since I 
first noted down facts relating to my Rhubarb I have no record of its 
being so late in producing as it has been th's year. Last year, 1890, it 
was indeed late. The first supply that was then brought to my table 
was on Feb. 22nd ; but this year the first I had pulled was in Mareh, 
the usual time for its being ready being as I stated {.Tox^rnnl of Ilorti- 
culture, July 5th, 1888, page 10), on St. Valentine’s day. To gardeners 
who know how greatly all out-of-door plants are influenced by the 
weather, and who remember the slight rainfall (black or Avhite) in last 
December, January, and February (February being nearly rainless), the 
unusual lateness of the plant this year will be no surprise, for my 
first gathering in 1891, which w.as of 3 lbs. weight, was on Thurslay, 
March 5th. Since then I have had it continuously, taking as much as 
12 lbs. at one time. My Rhubarb is grown in a bed perfectly open and 
exposed to all weathers, and perhaps on this account has come into 
bearing some eighteen days earlier than Mr. Pownall’s supply. 
I have only to add that I shall be happy to show anyone the Yaxley 
Rhubarb as it grows any week day by appointment, and as I am a busy 
man preferably between 9—10 A M. We are but one and a half mile 
distant from Mellis station.—W. H. Sewell, I'axleij Vicarage, Suffolk. 
ON THE EFFECTS OF URBAN FOG UPON 
CULTIVATED PLANTS. 
[Prelinunary report by Dr. F. W. Oliver, presente<l to the Scientific Commirtee of the 
Royal Horticultural Society, March 24th, 1891.] 
( Concluded from page 269.') 
V. Physiological and Microscopic Work. —The opportunity has been 
taken to have careful drawings prepared, exhibiting typical cases of 
damage attributable to fog. I have now a considerable collection of 
examples from the Royal Gardens, Kew, and elsewhere. 
Large supplies of injured plant organs have been forthcoming and 
have been submitted to chemical analysis. These include the leaves of 
soft and hardwooded plants and of Orchids, also the leaves of 
Cattleyas and Dendrobiums, and the flowers of Cattleya Trianie. The 
results of the,se analyses will be valuable for publication when similar 
analyses of the uninjured parts have been obtained. 
_ The histological characters of injured tissues, as exhibited by the 
microscope, have been carefully studied and drawings and notes made. 
Many of the facts thus obtamei are still obscure and require experi¬ 
mental elucidation. In the case especially of Orchid flowers the dis¬ 
tribution of the stomates would seem to have a definite bearing on the 
distribution of the fog injuries. In both Phalaenopsis Schideriana and 
Cattleya Trianse, for example, the sepals are much sooner and more 
easily injured than the upper petals and labellum. Microscopic 
examination shows that whilst stomates are frequent on the sepals of 
both plants, the petals have relatively few, comparing equal areas of 
surface. The labellum of Cattleya in many cases was found to be 
destitute of stomates. This part is usually the last to show actual 
injury. The action of the stomates here is probably to afford 
increased access of sulphurous acid to the part, which then directly 
attacks the soft, unprotected cells within. 
The* effects of a slow cunent of fog and of sulphurous acid of 
various dilutions upon living protoplasm have been very carefully fol¬ 
lowed under the microscope. The procedure in both cases was identical. 
A slow current was drawn by aspiration through a specially devised 
chamber on the stage of the microscope. The transparent root hairs 
of Limnobium, with their actively rotating protoplasm, and portions of 
the leaf of Vallisneria Avere ehiefly used. The effect of dense fog 
resembles very nearly that of dilute sulphurous acid. The rotating 
protoiilasm is found gradually to SAvell up and invade the vacuole, its 
defined margin becomes less and less distinct. Finally, the protoplasm 
becoming granular, and breaks doAvn entirely, the rotation during the 
process gradually slowing, ultimately ceasing. The Avhole process with 
fog occupies several hours. This line of research Avill be continued 
during the summer with sulphurous acid and other substances. 
A considerable series of experiments has been made in the closed 
chamber, which aams constructed for this, as also to serve as a fog-proof 
chamber for cultural purposes. As a fog-proof chamber it has not been 
used so far. At an early period I found that certain defects which 
could not be remedied forthwith disqualified it for this purpose. Since 
then it has served as a closed experimental case, in Avhich plants were 
exposed to sulphurous acid gas of varying strength. It was possible 
also to draw off a current of the special atmosphere, to which the plants 
in it Avere exposed, and study its action upon living protoplasm under 
the microscope. A comparison could thus be effected between the 
macroscopic and microscopic phenomena simultaneously. The amount 
of sulphurous acid present aa'us under control, and frequent estimates of 
its amount A\’as made by aspirating air from the chamber through 
permanganate, the volume required to decolourise being recorded. 
These experiments are not yet concluded, but it can be definitely said 
that increase of temperature, other things being equal, aggravates the 
poisonous action of the sulphurous acid, a difference of a few degrees of 
temperature being apparent. 
During the summer these experiments Avill be continued. An attempt 
Avill also be made to estimate the influence of varying amounts of sul¬ 
phurous acid gas and other poisons upon the plant functions—transpi¬ 
ration, assimilation, and resp'‘ration. 
VI. Possible Remedial Measures. —It is too soon to speak of these 
Avith confidence until a more complete knoAAdedge of all the conditions 
of damage to vegetation from this source have been obtained. Many of 
the results obtained in the physiological inquiry are still obscure, and it 
Avill be necessary to carry out series of experiments before some of these 
are elucidated. Since October I have had opportunity of inspecting many 
collections of stove and greenhouse plants, and growers have most freely 
communicated to me any methods Avhich they employ to combat the fog. 
The placing of canvas, &c., over the plant houses in foggy weather has 
in some instances mitigated the damage, the fog being in this way to 
some extent filtered. The regulation of the temperature has an important 
bearing. Some cultivators keep the temperature during a fog as low as 
can be done, having regard to the safety of the collections in the houses. 
Others raise the temperature in the hope of, to some extent, excluding 
the fog. There can be no doubt that a high temperature augments the 
damage, Avhilst a loAver one, to some extent, hinders it. 
Sulphurous acid acts more violently and immediately in a hot than 
in a cool atmosphere. Again, in a long, dark fog, heat unnecessarily 
stimulates the plants when (from the prevailing darkness) their tran¬ 
spiring capacity is limited. Everything should be done to tax the 
vegetative organs of a plant to the least possible extent when any of the 
vital functions are interfered Avith, as in dull, foggy weather. In this 
connection it is important to supply water to the roots with a sparing 
hand. Heat and moisture at the roots stimulate absorption, whilst the 
leaves are unable to throve off an excess of moisture, as they can in 
sunny weather. I know that in many establishments these precautions 
are taken, and I believe with relatively beneficial results. The evidence 
on Avhich this opinion is founded is derived (1) from observation of the 
behaviour of plants under different conditions of cultivation during 
foggy weather, (2) from actual experiments in which the special con¬ 
ditions were under control. 
The action of a continuous drip of moisture on foliage in a closed 
experimental chamber, containing small quantities of sulphurous acid 
gas, is to mitigate the immediate damage so far as the leaves, thus con¬ 
tinuously moistened, are concerned. 
The degree of humidity in a house, Avhere sulphurous acid is present, 
is a matter well worthy of attention, and one which I have under obser¬ 
vation. The problem is a complex one, and I hope to be able to com¬ 
municate my results later. 
In a dry atmosphere the sulphurous acid, for the most part, acts as 
such directly on the living protoplasm. In a humid one it is more 
rapidly oxidised into sulphuric acid, Avhich has an entirely different 
action, I apprehend, on vegetation, histologically distinct from the first 
mentioned. It would, however, be improper for me to draw any general 
conclusions from observations as yet incomplete. 
Another measure, Avhich may be ultimately shown to he practicable, 
is that of absorbing the most poisonous substances in the fog by using 
some substance as an absorbent, itself innocuous to vegetation. 
A more practical method is to keep the fog out of the plant house, 
rather than to try and neutralise its action after it has entered. So 
long as cultivators groAv plants susceptible to the impurities of fog in 
houses with open glazings in winter time, of course this is impossible. 
It is to be hoped some metropolitan groAver will pluckily face the 
situation and construct a range for Avinter use, Avhich can be made at 
Avill absolutely fog proof Avith close glazing, triple doors, and padded 
ventilators. The horticultural engineer could easily manage this. 
Filtered air could be supplied, as it is to the House of Commons, by 
pumping through several inches of cotton wool or by some other 
method ; whilst the illumination could be supplemented by a judicious 
use of the electric light. Herve-'Mangin showed, so longagoas 1861, that 
a plant could manufacture organic matter by the aid of artificial 
