The Law of Relative Constancy of Habitat—Ecotypes and Ecoclines

Abstract

Many species are very widely distributed and grow under apparently very different climatic conditions. Waterplants have, to some extent, a very cosmopolitan distribution, but this is due to the fact that all over the world they find habitats where very similar conditions prevail. An example of this is the rigid hornwort, Ceratophyllum demersum, which grows not only in tropical waters but also in those of zones with a cold winter. In the latter, this plant forms dormant winter buds (turions) and overwinters at the bottom of the lake or pond. Annual weeds require only a short period for their development in biotopes where there is no competition; these may be fields in arid areas with a short rainy period, or in those areas in temperate zones which have short, hot summers or, frequently, uncultivated soils in warm climates.