72 
THE GARDENING WORLD 
January 24, 1903. 
are the lower branches removed to any particular height, as 
the bare trunks range from 7 ft. to 18 ft', above ground before 
they are allowed to put out lateral branches. Evidently this 
peculiar form of rule of thumb has no connection either w ith 
line or rule. 
Mr. Simpson also complains that the pavement is too close 
to the tree to allow of swelling or of water getting to the 
roots. As a rule, a square or circular space is left round the 
base of trees in London and its suburbs, and frequently a piece 
of iron grating covers the space, and permits of foot-traffic 
passing uninterruptedly over the same. As far as the watering 
of the roots is concerned, we think this piece of grating a matter 
of moonshine, because the real feeding roots of trees that 
have been some years established are far byond the 1 influence 
of any water that may be poured into the little basin around 
the base of the trunk The feeding roots of trees in the High 
Road, Chiswick, must extend far beneath the stone pavement 
that carries the foot passengers on the one hand, and the wood 
paving that hears the road traffic on the other. The old 
Lime trees in the Duke’s Avenue present a more serious case, 
for the roadway consists of asphalted concrete. The question 
arises how the roots of those trees can manage to get either air 
or moisture. The most feasible explanation is that the supply 
of the latter is kept up by capillarity from beneath, and from 
lateral directions where open garden ground still exists, and 
that the asphalt paving prevents the loss of water except 
through the channels of the roots and the trunk of the trees 
to the leaves, and thence into the air. Under such circum¬ 
stances, it may be that the paving is conservative of moisture. 
Mr. Simpson, in the case of the trees at Worthing, says that 
each kind of tree should be trained to copy Nature, and have 
its special requirements as to pruning. A Birch, Acacia, or 
Cornish Elm would never spread like a Chestnut, Sycamore, or 
Plane, and hence would not occupy a similar amount of space. 
It is rather drastic criticism when lie says that many of the 
trees lately planted are not worth the labour expended upon 
them nor the stakes that support, them. Furthermore, he 
contends that trees planted in confined spaces would require 
pruning twice a year in order to keep them within due bounds, 
and also to regulate the density of the branches and foliage.' 
This is exactly the contention at which we aimed above with 
regard to the trees in the narrower streets of Chiswick. Severe 
pruning to keep the trees within due bounds has the effect of 
causing the development of far too many rampant shoots for 
the space at their disposal. The removal of the superfluous 
ones at an early stage> of growth would permit of proper 
development of those that are left, and also allow the foliage 
to receive its due share of illumination. 
The trees recommended by Mr. Simpson as suitable for 
road planting are Elm, Lime, Sycamore, Maple, Sorbus (Pyrus 
Sorbus and P. Aucuparia, we presume), Birch, Acacia, and 
Beech. In narrower ways and streets we should also recom¬ 
mend the smaller varieties of the English Elm, the Kilmarnock 
Willow, Weeping Beech, and fastigiate trees like the Lombardy 
Poplar, erect Robinias, Oaks, White Poplar, and others having 
erect growing varieties. The White Willow (Salix alba) is a 
very handsome tree, and readily conforms to trimming with 
the knife in order to restrict its extension either laterally or 
in height. 
Acetylene Gas-light and Plants. 
From time to time various experimentalists have turned their 
attention to the effects which .artificial lights have upon plant 
growth, having in view the possibility of employing artificial 
illumination as a means of forcing commercial vegetable crops 
grown under glass. The electric arc lamp has been tried, and, 
according to at least one large grower, W. W. Rawson, of Arling¬ 
ton, Mass., with successful results. Indeed, in a recent letter 
from that gentleman we are informed that he finds the installa¬ 
tion still satisfactory under his conditions. 
The incandescent gaslight was made the basis of a very careful 
series of experiments by Professor Corbett, now of the U.S. 
Department of Agriculture, and fairly good results were ob¬ 
tained, but as to whether there would be a profitable result in a 
commercial way cannot be told 
Still more recently Professor F. W. Rane, who has identifiel 
himself with experimental vegetable forcing at the New Hamp¬ 
shire Station, has conducted a series of tests, using the acetylene 
gaslight as the extra illuminant. 
A ten-pound Acetogen generator, with accompanying equip-. 
ment, a cluster of eight burners, and a large twenty-inch re¬ 
flector, were installed in onie of the forcing houses in the spring 
of 1899. 
The cluster of lights was placed directly over one end of the 
bed, and was turned on April 4, 1899, and allowed to run each 
might, the number of hours being noted. 
One-half of the bed was curtained off during the night, so that 
with the exception of the exposure to the light, the conditions 
were precisely similar. At the expiration of the experiment, on 
May i, the effect of the light was more or less marked upon the 
growth of Beets, Spinach and Cress, but less evident upon Peas. 
Tomatos and Potatos. The Lettuce was, perhaps, a trifle taller 
under the light, although njot very perceptibly so. It was also 
more tender. Not much, if any, difference could be seen with 
other plants, such as Beans, Radishes, etc. 
The experiments were continued a second season. On December 
28th a large bed was prepared and.planted. On; January 1st the 
lights were started and run each night until the experiment was 
concluded on February 15th. 1901. 
The first perceptible signs of any beneficial effect of the light 
were shown on January 8th, whenl .some of the plants, particularly 
Lettuce, began co show an increase in growth. While the Lettuce 
seemed to grow taller, ilfc also tended to greater tenderness. On 
January 10th Beans, Parsley, Radishes and Coleus showed the 
effect of the light, and were a trifle taller and more slender. 
January 16th there was quite >a marked difference on Lettuce, 
Parsley and Beans under the light, but mot so much with other 
plants February 9th measurement of each individual plant was 
made and their averages calculated. 
Under light. In dark. 
{St 
1 1.9 inches. 
8.2 „ 
10.3 inches 
6 5 „ 
{ I'™'’!, 1 ,. 
10.7 
6.8 
!5 
J? 
11.3 „ 
5.4 „ 
Coleus 
height 
11.7 
>) 
10.0 „ 
Beans 
height 
14.4 
11.9 „ 
The Radish leaves were taller, having longer petioles, under the 
light. The corn was also taller under the light, but looked 
more stocky and had better colour in the dark. 
Until this time the eight lights, .allowing for occasional deduc¬ 
tions due to broken fixtures, etc., had run 446^ hours. 
On February 14th the last measurements were made, but did 
not show much difference from those of February 9th. 
At the conclusion of the experiments on February 15th the 
Lettuce crop was cut and weighed. The Lettuce in the light out¬ 
weighed that in the dark by only ^ lb., 14 heads being taken in 
each case. The greatest, difference was in the height. The main 
central stalk of the Lettuce in tire dark was short in every case, 
2^ inches being the longest, while the average was less than one 
inch. Under the light the longest was 51, inches, and the average 
was between 3 and 4 inches. 
Without going further into detail, the following deductions as 
reported by Professor Rane may be made from the experiments 
thus carried on ; — 
1. That the acetylene gaslight has a marked effect upon green¬ 
house plants. 
2. That no injurious effects resulted from the use of the 
acetylene gas-light. 
3. The light has a stimulating influence on most plants, and 
appears to be beneficial to some plants that are grown for foliage, 
such as Lettuce. The Lettuce stood more erect and weighed 
more. 
4. Most plants tend toward a taller growth under the light. 
5. It. is doubtful whether this light can be used in the green¬ 
house from an economic standpoint for growing plants alone. 
While its effect is marked in the dark days of winter, little dif¬ 
ference seems to be shown at other seasons of the year, when 
there is more sunshine. 
6. There are many points about the acetylene gaslight that 
make it desirable for lighting greenhouses. It is not expensive, 
is easily piped, and comparatively simple to run. 
