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The European frost-weeds or Helianthemum include a group of species which are so closely allied, that ordinary botanical descriptions are not adequate to give any idea of their differentiating features. It is almost impossible to determine them by means of the common analytical keys.
From time to time the halved plants were compared with each other, and the cultures lasted, as a rule, during the lifetime of the individual, often covering many years. The common European frostweed or Helianthemum vulgare will serve to illustrate his results. A large plant growing in the Pyrenees in an altitude of 2,400 meters was divided.
They have to be gathered from their various native localities and cultivated side by side in the garden to bring out their differences. Among the species of France, according to Jordan, Helianthemum polifolium, H. apenninum, H. pilosum and H. pulverulentum are of this character.
There is no danger that lamarckiana might die out from the act of mutating, nor that the mutating strain itself would be exposed to ultimate destruction from this cause. In older swarms, such as Draba or Helianthemum, no such center, around which the various forms are grouped, is known. Are we to conclude therefore that the main strain has died out?
On the contrary we find elementary species in different genera based on the greatest possible diversity of features. The forms of Taraxacum or Helianthemum do not repeat those of Draba or Viola. In roses and brambles the distinguishing features are characteristic of the type, as they are evidently derived from it and limited to it.
It is perfectly hardy, and grows freely in porous decomposed leaf-soil. HELIANTHEMUM HALIMIFOLIUM. Spain, 1656. This species is of erect habit, 3 feet or 4 feet high, and with leaves reminding one of those of the Sea Purslane. It is an evergreen, and has large bright yellow flowers, slightly spotted at the base of the petals. South-western Europe.
Arabis stricta occurs only on the limestone near Clifton; Helianthemum polifolium is confined to Somerset and Devon; Pirus latifolia to Somerset and Denbigh. For the birds of Somerset, see a paper by the Rev. Murray A. Mathew, M.A., F.L.S., in the "Proceedings of the Somerset Archaeological and Natural History Society," vol. xxxix., from which we have borrowed.
Let us begin with the sharpness of the varietal characters. In this respect varieties differ most obviously from elementary species. These are distinguished from their nearest allies in almost all organs. There is no prominent distinctive feature between the single forms of Draba Verna, Helianthemum or of Taraxacum; all characters are almost equally concerned.
In Helianthemum the capsule has been described as unilocular or tri-locular; and in H. mutabile, "Une lame PLUS OU MOINS LARGE, s'etend entre le pericarpe et le placenta." In the flowers of Saponaria officinalis Dr. Masters has observed instances of both marginal and free central placentation. Lastly, St.
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