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Botanical: Chrysanthemum roseum (ADAM), Pyrethrum roseum (BIEB.), Chrysanthemum carneum
---Synonyms---Insect Flowers. Insect Plants.
Family: N.O. Compositae
---Part Used---Closed flowers.
The Insect Powder of commerce, used to stupefy and kill various small insects, especially the larvae of Cochylis, which attacks the vine, was first known as Persian Insect Powder, or Persian Pellitory, being prepared from the closed flowers of Pyrethrum roseum and P. carneum, plants native to the north of Persia, where they flourish on the mountain slopes up to a height of 6,500 feet, and also in the Caucasus. These two species are familiar in this country as garden flowers, of which there are many varieties in cultivation, blossoming freely in May, the tufts of foliage of a dark green, much cut into, and the flowers of all shades of rose and crimson.
Some years ago, a Dalmatian species, Chrysanthemum cinerariaefolium, was found to be more active, and the Persian or Caucasian Insect Powder Plants are now seldom imported, being superseded by the Dalmatian species, which has white flowers, smaller than our Ox-Eye Daisy. It is cultivated both in Dalmatia and in California.
The cultivation of the Insect Powder plants has not yet been taken up on a commercial scale, either in Great Britain or the colonies, but it could be grown successfully in certain districts in this country.
There is a great demand for the flowers in commerce, and the flowers received from their usual source are so frequently adulterated by the addition of other composite flowers which are lacking in stupefying power, that the cultivation of the plant would be most desirable, either here or in our colonies. It can be profitably grown on dry, stony soil.
The conditions suiting the Dalmatian variety are sunny, pebbly, calcareous hillsides, dry, without irrigation, and in a fairly dry atmosphere. In ordinary garden soil, it does not flourish in shade and often dies off after flowering. All three species grown experimentally at Berne often succumbed during moist summers.
On the warmer southern and western coasts of Great Britain, the plant could easily be cultivated. It might be grown with success on the hilly slopes of oolite and limestone and chalk and on sandhills on the shore in Cornwall, Devon and Lancashire, or on the pebbly beach of Lydd, in Kent. In Jersey, on the pebbly and sandy shores, it would grow luxuriantly.
Attempts have already been made to cultivate the plant in Australia and South Africa.
Insect Powder is harmless to human beings. Besides being used as an insecticide in the form of a powder, it is also used as a lotion, a tincture of the flowers being prepared and used, diluted with 10 parts of water, to dab on the exposed skin to keep away insects. It is also employed as a fumigator. The smoke of the burnt flowers is as effective as the powder in keeping down insects, and might be valuable in Africa as a means against the tsetse-flies, and in sleeping sickness districts, if grown on the shores where they breed, and burnt when the flies emerge from the chrysalis.
In Dalmatia, the plant grows on the seashore, but it also grows well in the inland, mountainous districts of Herzegovina and Montenegro, the wild Montenegrin flowers being very highly esteemed. In the Adriatic islands, its cultivation is very remunerative.
---Cultivation---Sow seeds at the end of March on rich, light soil, in sunny situation and cover with 1/4 to 1/2 inch of fine soil and then with dry leaves. If the autumn be mild, the seeds may also be sometimes sown in August, or early September, as soon as the seed is ripe, but then they need shading with canvas, placed about 6 inches above the soil, or more. Prick out the seedlings in the following March, or later, if sown in September. On the average only about half of the seedlings are fit for pricking out.
It is difficult to obtain seed that will germinate, the Dalmatian growers apparently dry the seeds by heat before disposing of them, to prevent germination.
Arrange the plants in deep furrows, prepared the previous autumn, about 15 to 20 inches apart, the seedlings 15 inches apart in the furrows. Of every 100 plants pricked out, fifteen to thirty generally die off and have to be replaced.
Weed several times during growth.
The plants begin to flower about the third week in May. The flower-buds are collected in the middle of May, or if it should then be damp, not till June. They must always be collected in dry weather.
A second gathering is made in August and September. The unopened flower-buds are kept separately, as they obtain the best price. The flower-heads are collected at different stages of development, the commercial varieties being known as 'closed,' 'half-closed' and 'open' flowers respectively. They are most active if collected when fully developed, but before they have expanded. They are cut off just below the involucre of bracts.
The flowers retain their insecticidal properties for an indefinite period, if kept under suitable condition, even if in the state of dry powder. It is the flowers alone that are active; the leaves have no insecticidal properties whatever.
The powder prepared from the Dalmatian flowers is distinguished from that of Persian flowers by numerous hairs. The better the quality of the powder, the larger will be the proportion of pollen and the smaller the proportion of stem issue.
One of the best tests of the quality of the powder is to keep a few house-flies under a tumbler with a little of the powder; they should be stupefied within a minute. Adulterated or less active powder will take about twenty minutes to effect this.
Each plant yields 80 to 100 flowers, and in one day 1,500 to 2,500 flowers can be gathered by one person. One hundred flowers weigh about 50 grammes (1 5/3 OZ.). One hundred kilos (220 lb.) of fresh flowers yield 25 to 33 kilos (55 to 72 lb.) of dried flowers.
In Dalmatia the flowers are dried in the shade on frames of cloth, in layers 1 to 1 1/2 inch deep, turned over two or three times daily. The Persian flowers are dried first in the sun and then in the shade.
After harvesting, the land is tilled in the autumn and again in the spring, the soil being forked between the rows to keep it porous. Being a mountain plant, it requires a dry surface, well drained below. Sunlight and heat are necessary for luxuriant growth.
The plants live on the average for six years, but sometimes will remain healthy and strong for as much as twenty years.
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Bear in mind "A Modern Herbal" was written with the conventional wisdom of the early 1900's. This should be taken into account as some of the information may now be considered inaccurate, or not in accordance with modern medicine.
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