POPULATION STUDIES ON VIOLA LACTEA SM. AND ITS WILD HYBRIDS

Viola lactea Sm. belongs to the group Arosulatae of the sub-section Rostratae, section Nomimium (Becker, 1910). Its distribution is "Oceanic West European" (Matthews, 1955) and it occurs in scattered localities from the south and west of the British Isles, down the Atlantic coast of France and through N.W. Spain, to ireach its southern limit in Portugal about the River Tagus (39?N)). It is typically a member of the "atlantic" heath communities of Western Europe and inhabits dry, acid, rather sterile soils. The detailed ecology is described elsewhere (Moore, 1958). Compared with the eurasiatic distribution of V. canina L. (Group Arosulatae), the restricted range of V. lactea seems primarily due to climate since its eastern boundary does not extend beyond the 380 F. January isotherm. Where climatic conditionls are such that the species are likely to come together, as in S.W. Britain, their differing edaphic requirements have been shown to influence their choice of habitat (Moore, 1958). The most important of these was found to be the base status of the soil; exchangeable calcium is high in soils with V. canina (19.17 ? 4.293 m.equiv./100 gms. soil) and low in those with V. lactea (5.11 ? 2.719 m.equiv./100 gmns. soil). Other factors of importance include competition from associated species, biotic influences and physical stability of the substrate. V. riviniana Rchb. (Group Rosulantes) is found over the whole of Europe and has been shown (Valentine, 1949, 1950) to