The Ecology of Rare Plants

Rare plants, though the chief initerest, of taxonoamists, have been almost wholly ignored by ecologists. This is easy to unlderstand. The collector journeys far to get rarities to complete his herbarium, but since they seem to cutt no figure ill the vegetation as a whole, they do not ordcinarily enter the horizon of the ecologist at all. Yet I believe the stu-ldy of rare plalnts can add m-uch to our undlerstanding of ordiinary vegetation; for I have come to think that the explanat,ioni of the oceurrenee of rare plants, which has puzzled botanists from time immemorial, will contribute to an unclerstandcling of the vegetational history of their habitats. Certainlyl T rare plants in many cases are not isolated, incdividcual phenomella, but their presence is a characteristic feature of the ecology of the areas ill which they oceur; for it is a curious fact that rarities grow together, certain areas being especially rich in plants not to be founld elsewhere for long clistaiices. Every workinig botanist will call to miicl cases from his oWln experienee. The problem of the ecologist, then, is to aseertain the reasonl for the congregation of rarities into special localities. In this paper there is offered for more general testing a working hypothesis for the concentiration of rarities together with the da,ta which suggested it.