This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
The Single dahlias may be freely produced, but they are not so lasting for cut-flowers. The Single type has had many ups and downs. In the reaction against formalism, it came to the front about 1881, and for several years thereafter several hundred forms were kept distinct and they were made the chief feature of the European shows. When the dahlia first came into cultivation, its rays were relatively long, slender, acuminate, notched at the end, and with such wide spaces between the tips of the rays as to give the flower a stellate appearance. In the course of the evolution of the single type, the gardeners retained the most regular and symmetrical forms. Single dahlias with always and only eight rays were preserved. The rays of dahlias became broader and rounder, as in Fig. 1214, until finally in pedigree varieties the vacant spaces were closed up. The same mental ideals have produced the rose-petaled geraniums and the shouldered tulips. In a high-bred single dahlia there are no minute teeth or notches at the tips of the rays.
Most of the single dahlias of high pedigree have rays of uniform coloration with no secondary color at the base, but a few have a distinct ring of color at the base, often called an "eye or crown," which is sometimes yellow and rarely red or some other color. Usually the rays of a single dahlia are spread out horizontally, sometimes they bend back, and rarely they bend inwards and form a cup-shaped flower. These three forms can doubtless be separated and fixed during those periods when the interest in the Single type warrants it. Semi-double forms are frequent (Fig. 1215).
Single dahlias are likely to lose some of their rays after a day or two in a vase. In cutting them it is well to choose the younger flowers. A vigorous shake often makes the older ones drop their rays. It is an easy matter to keep the seeds from forming, simply by removing the flowers as they mature, and by so doing save the strength of the plant for the production of flowers.
There are three other dahlia types of minor importance,-the Single Cactus, the Pompon Cactus and Tom Thumb. The Single Cactus type differs from the common Single type in having rays with recurved margins, which give a free and spirited appearance to the flowers. Instead of spreading out horizontally, the rays often curve inward, forming a cup-shaped flower. This type originated with E. J. Lowe, Chepstow, England, was developed by Dobbie & Co. about 1891, and was first disseminated in 1894. The Single Cactus dahlias are very interesting and pretty. The Tom Thumb type is a miniature race of round-rayed single dahlias, which grow from 12 to 18 inches high, and are used for bedding. The type originated in
England with T. W. Girdlestone, and was developed and introduced by Cheal & Sons.
Fig. 1209. Dahlia Merckii.
Redrawn from the Botanical Magazine, for 1841.
The "green" dahlia (Dahlia viridiflora, Hort.) is an interesting abnormal form in which the rays are partially or wholly suppressed, and the chief feature of interest is a confused mass of green, not resembling petals at all, but evidently a multiplication of the outer involucral scales, which, in the dahlia, are green, leafy bracts. The "green" dahlia is not unhealthy; it is as strong and vigorous as any of the other forms, but very unstable and variable, producing flowers of solid green color, others of green with small cup-shaped crimson-scarlet petals intermingled, and others of solid crimson-scarlet color, and all on the same plant. This freak was pictured as'long ago as 1845 in G.C., p. 626; and again in G.C. III. 30: 294.
Another interesting variation which hardly ranks in present importance with the eleven types contrasted below is the laciniated form, which makes a very pretty though rather formal effect. Examples are Ger-mania Nova, Mrs. A. W. Tait and its yellow variety among large double forms, and White Aster among the Pompons. In these cases, the notches at the tips of the rays, instead of being minute and inconspicuous, are deepened so much that they give the laciniated effect. At present this form is available in a very narrow range of colors. It is not probable that it will be an important factor in producing chrysanthemum-like forms.
Another form which baffles description, but is nevertheless very distinct, is that of Grand Duke Alexis. It is nearer the Show type than any other, but is perhaps best classed with the Cactus Hybrid section, simply because it seems advisable to keep the Show type the most sharply defined of all. It is a very flat flower, and the rays are remarkably folded, leaving a round hole at the top of each one. Up to 1909 the variety of colors of the type of Grand Duke Alexis has been increased, including the varieties Dreer White, Mrs. Roosevelt, Purple Duke, Pythias, W. W. Rawson, and Yellow Duke.
About midway between Grand Duke Alexis and the Show or cupped type is an interesting form, the "quilled" dahlia, a name which is perhaps necessary, though unfortunate. In A. D. Livoni the rays are rather tightly folded for about two-thirds of their length, leaving a round hole at the tip as in Grand Duke Alexis, but giving a peculiar whorled effect, which plainly shows the spiral arrangement of the successive tiers of rays. Among Pompons, Blumenfalter is an example of this rosette-like or quilled form, and many colors are procurable. However, the word "quilled" usually suggests a long tube with a flared opening, whereas in the form described above the margins of the ray are merely rolled tightly together, but not grown together into a thin seamless tube. Perhaps the most important variation that has not yet appeared in the dahlia is the wonderful elongation of the disk florets into long, thin, variously colored tubes which have produced such charming effects in the China aster and have culminated in the marvelous grace of many chrysanthemums.