294 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
[ April 14,1887. 
by Johnson give respectively sixty-four, eighty-three, ancl seventy-seven 
per cent, of silica. Going back to 1840 Sir Humphrey Davy says, 
i: Silicic acid occurs. . . . and forms a large t art of almost every 
soil.” If these authorities are right, I do not think we “ need trouble 
much about silica.” 
Now to another little matter. Mr. Abbey, I think, may fairly be 
understood to infer that land cannot be kept up to the mark or improved 
by means of artificial manures alone. If the readers of the Journal are 
interested in the matter they may be surprised to hear that on clay land 
near Sawbridgevvorth, in Hertfordshire, a gentleman named Prout has 
been growing corn, crop after crop, rather extensively too, on the same 
land, using only artificial manures (something besides the ammonia 
salts though) since 1861. He has acted under the advice of Dr. Voelcker, 
who states that the soil is now richer and in a better state to produce 
corn than it was the first year of the experiment. 
I grow Roses, or try to do so, and I admit that up to now my experi¬ 
ence is like that of the old farmer, that “ there’s nothing like muck,” 
but in the time to come I look forward to the production of Roses and 
all other crops, whether for the gratification of our mental or physical 
appetitespby means of artificial manures properly applied, and with a 
full knowledge of the constituents of the plants and flowers we wish to 
produce.— D. Gilmour, jun. 
THE COLOURS OF LEAVES AND FLOWERS. 
The fifth lecture of the season at the Lincoln School of Science was de¬ 
livered by Dr. G. M. Lowe recently, the subject being “ The Colours of Leaves 
and Flowers.” A number of experiments added greatly to the interest of the 
lecture, which was further illustrated by diagrams, &c.; valuable assistance 
being also rendered by Mr. Henry Mantle with bis oxy-hydrogen lantern. 
A beautiful collection of choice plants and flowers was likewise kindly lent 
by Mr. Joseph Ruston for the purposes of the lecture. 
Dr. Lowe said that fortunately for him the most difficult part of his sub¬ 
ject, that of light, had been carefully explained by Dr. Griffiths in that room 
a fortnight ago ; therefore, it was only necessary for him to refer to that 
point very briefly. What he wished them to remember was this, that white 
light, streaming from the sun upon the earth, gave to natural objects an 
immense variety of colour, which disappeared at sunset, or when the light 
•was withdrawn. If, instead of sunlight, the white light derived from burn¬ 
ing magnesium, the oxy-hydrogen limelight, or the el c trie light, was sup¬ 
plied, the colours were again manifested ; but if the light of the coal gas 
flame was substituted, then many colours, such as the violet and purples, 
were altered, or were altogether lost. This fact was still more strikingly 
shown by means of the yellow light of the sodium flame. He also pointed 
out that if a ray of sunlight was received on a properly arranged prism, it 
was immediately broken up into the colours of the rainbow; it was, in fact, 
analysed ; and if a white screen was placed at a convenient distance, the 
colours would be received upon it, and could be examined. Those colours, 
they would see on the diagram, were red, orange, yellow, green, blue, indigo, 
and violet. It would be observed at once that green occupied the centre of 
the system, and from it the colours ran through blue to violet on the one 
aide, and through yellow to red on the other. He called especial attention 
to this fact, because it greatly explained his case. Green combined in vary¬ 
ing proportions with blue or violet would produce one set of colours, and, 
similarly, green combined with red produced an entirely different class. He 
(the lecturer) did not know of a single instance in the whole range of the 
vegetable kingdom where those two classes were visibly mixed. 
If a green leaf was examined optically by means of the modified prism 
called a spectroscope, it was found that extreme red was present; then 
occurred a deficiency of coloured light, followed by orange red; next came 
orange, then the yellow, greenish yellow, and yellowish green ; after that 
followed a little full green, the rest of the spectrum consisting of a little 
weakened blue and violet. They would recollect that all these colours 
existed in a green leaf, but yet that it appeared green. An inspection of 
the diagram showed that the yel’ow occupied a position b< tween the red 
and the green. This suggested the probability that the yellow was a com¬ 
bination of those two colours, and this was found to be so by experiment, 
for although red and green pigments would not by mixing form yellow, it 
might be obtained in other ways, either by using two prisms, or by placing 
red and green colours on a disc and rapidly rotating it. This was demon¬ 
strated by two prismB, and by means of rotating colour discs. By making 
a disc composed of red and green—50 per cent, of each—taking the semi¬ 
circular form, and laid on a black ground, on setting the disc in ranid 
motion a yellow was the result. The lecturer here paused to point out that 
the old theory maintained by Sir David Brewster that yellow was a primary 
colour had exploded, as it had been shown that yellow was a compound 
colour, composed of red and green. On the other hand, it was proved that 
green, which was formerly regarded as a compound colour, composed of 
yellow and blue, was a primary colour, for it was impossible by mixing the 
coloured lights from any known yellow and blue surfaces to form green. 
On setting a zone of yellow and blue in rotation, they found accordingly 
that, instead of green, whit: light was produced. Hence the three primary 
colours were green, red, and blue—not yellow, red, and blue. Reversing 
the spectrum of a green leaf, they found the result was a yellowish green— 
as it was generally seen by daylight. 
Although it seemed reasonable to assume that vermilion and emerald 
green, combined in certain proportions, would produce leaf green, it was 
found that an important element must be added—viz., black. Black entered 
argely into the structure of leaves, and its presence was not difficult to 
account for. On examining the lower surface of a leaf by the aid of a micro¬ 
scope, thousands of little openings or mouths were seen, called stomata. 
As many as a quarter cf a million had been computed in a single square inch 
of the lower suiface of a Lilac leaf. It was through these openings that the 
carbonic acid, which was so largely distributed throughout the atmosphere 
by the respiration of animals, was absorbed. It appeared to enter in a 
gaseous state, passing into the cells, where it became chemically decom¬ 
posed into its two elements, carbon and oxygen ; the carbon was retained 
and blackened the leaf, and the oxygen was set at liberty to purify the air 
They had now three elements to start with ; and by way of preliminary 
trial the lecturer placed them in varying relative proportions on discs, and 
set them in rapid motion. The first disc, red and green in proportions of 
one red to two green on black ground, produced leaf green. But if the 
proportion were so altered that the red preponderated, the green quite dis¬ 
appeared, as in the following disc, which represented the reddish brown 
tints of autumnal leaves, as in the leaf of the Hornbeam—red 20, green 10, 
black 70. When equal, the yellow element prevailed, and the browns 
partook of cinnamon in their colour. 
The lecturer said he would now gently touch on a difficult subject. In 
addition to the colours reflected from surfaces, there was also reflected a cer¬ 
tain quantity of white light, and different colours reflected different quanti¬ 
ties of white light, which was called their luminosity. Thus, taking the 
luminosity of white paper at 100, emerald green reflected 48'6 per cent., 
English vermilion 25'7 per cent., and so on. They would here inquire why 
a leaf was gr<:en, a Geranium scarlet, or an Arum Lily white. In a globe 
before him was a fluid which appeared perfectly black. By adding pounded 
chalk it changed immediately to a blue colour. Why was that ? Because 
the white particles acted as mirrors to reflect the light, and reflected the 
light after it had gone to some depth in the fluid. This was what took 
place in the green leaf and petals of flowers. In the case of the white Lily, 
if the petal was a sheet of thin glass, they would not have seen that white 
colour; a little light would be reflected from the front and back surface, 
but the petal of the Lily was composed of a vast assemblage of little cells, 
from the walls of each of which partial reflection took place, so that it 
resembled finely powdered glass, which appeared white because each little 
surface reflected the light, although a polished sheet of glass would not be 
white. The little cells of the Lily resembled the minute fragments of glass, 
and reflected white light. The same thing took place in the case of the 
Geranium ; the light was absorbed and reflected by the cell surfaces, but the 
light became tinted by the coloured juices in the cells of the leaf structure. 
It would therefore, said the lecturer, be easily understood that a certain 
amount of light escaped the influence of the colouring matter, and what 
was reflected from this was luminosity. A method of estimating the 
amount of luminosity had been discovered by Dr. Gorham, of Tunbridge, 
to whom he (Dr. Lowe) was indebted for much valuable assistance in pre¬ 
paring this lecture. Dr. Gorham effected this by means of a circular zone, 
composed of equal parts of white and black—which when set in rapid 
motion gave a grey—which was the medium grey of scientists, the half 
tone of artists. Its utility depended on the property it possessed in common 
with other grey tones of developing and rendering visible to the eye the 
complementaries of colours, and of black and white. What was a comple¬ 
mentary ? It was that which was wanting in a given colour to complete or 
supply the deficiency of white light. White light was composed of seven 
colours ; four were composed by intermixture of the other three, which were 
called primary—viz., red, green, and blue—which together made white light. 
If they took any one of them, the other two mixed gave the complementary 
colour. This was practically tested by interposing pure grey between the 
eye and the colour, the complementary colour being found to be of pink, 
green; of green, pink ; of white, black ; of black, white. By means of the 
ring it was possible to test exactly the amount of luminosity given off by 
coloured surfaces, and still further by haves themselves, and thus to esti¬ 
mate the proportions of the colours that made up the tint of the leaf or 
flower under examination. * 
The lecturer went on to inquire a little into the cause of the colours o 
leaves and flowers. Taking green as the basis, they found it the universa 1 
tint throughout the vegetable world. It appeared to be due to the presence 
of a highly organised substance called chlorophyll, or leaf green, which was 
not soluble in water, but highly soluble in alcohol and bisulphide of carbon. 
It was transparent in solution, and underwent change of colour under cer¬ 
tain conditions. Chlorophyll appeared to bear similar relations to plant 
life that blood does to animals. Under the influence of light it decomposed 
the carbon and oxygen into its elements, and elaborated the juices of plants. 
In the absence of light it changed to a lighter colour. In the presence of 
vegetable acids, such as tartaric and malic acids, it passed from a green to 
a yellow, an orange, cr a red. In this condition it appeared to lose its vital 
or chemical influence over carbon and oxygen, as oxygen appeared not to be 
evolved from coloured leaves and flowers. In the presence of alkalies, chlQ- 
rophyll was converted into green blues, blues, purple, and violet. Vege¬ 
table colours generally showed these peculiarities with regard to acids and 
alkali's, the blues becoming red under the influence of acids, and the reds 
blue on the addition of alkalies. The nearer the colour was to green the 
less sensitive to their influence it became, green itself remaining obstinately 
green or yellow brown unless operated on in its living state. The remark¬ 
ably beautifully colours of flowers was, with the exception of garden varie¬ 
ties, the result of the survival of the fittest. Since the days of Darwin 
they had ceased to say that the ornamentation of plants and animals was 
for the delight of mankind. Of all created beings man alone was inde¬ 
pendent of colour, whilst to plants and fishe9, birds and insects, quadrupeds 
and reptiles, colour was essential to their existence as species. The bril¬ 
liantly coloured petal or leaf of the plant was Nature’s signal to the nectar¬ 
eating insect that the repast was ready, but the entrance to the refectory 
was to arranged that the recipient must perform the work of the fertilisa¬ 
tion of the plant in repayment for its meal. When the flower was incon¬ 
spicuous, coloured leaves acted as the decoy, the Poinsettia and the Croton 
being examples. Plants that had no such attractive colours would often 
be lost but that they had other means of propagating their species, as by 
limners or suckers underground—the Nettle, for instance. Cultivation un¬ 
doubtedly also determined the colours of leaves and flowers—the first by 
appropriate feeding, the latter by selection and cross-fertilisation. Experi 
meets in cultivation by starving and feeding were in operation, and he (the 
lecturer) hoped to have an opportunity of describing the results on some 
future occasion .—(Lincoln Gazette.) 
ROYAL CALEDONIAN HORTICULTURAL SOCIETY. 
The spring Show of this old established Society was held in the 
Waverley Market, Edinburgh, on the first Wednesday and Thursday of the 
