Effects of radiation on growth and development
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H. A. Borthwick and S. B. Hendricks. With 7 figures.
lntroduction. Aspects of plant growth in response to radiation other than those immediately associated with photosynthesis and tropic movements are subjects of the following chapters. Efforts have long been made to recognize the several modes of action of radiation on growth, and the lines along which the subject has advanced are shown by the individual chapters. The conclusion, however, cannot safely be drawn that all photoresponsive systems affecting plant growth, particularly those that may be effective at high light intensities under normal conditions of growth of many plants, have been recognized. Effects of daylight on the internode lengths of phanerogams were possibly the first growth responses of plants to radiationtobe noted. Observationsare chiefly of two types: namely, those on dark-grown seedlings irradiated for short intervals and those on older plants growing in shade, a limited part of the sun's spectrum, or with radiation from sources other than the sun and often of low intensity. The formative effects are more general than those commonly noted on internode lengths and are particularly evident in growth of leaves. Other responses to radiation to be considered are associated with the photoresponsive system of photoperiodism and with that of phototropism at both high and low intensities. The photoresponsive system upon which photoperiodic control of flowering depends is effective also in light control of seed and spore germination and in a nurober of other aspects of growth. Effects on growth of exclusion of light or of light deficient in certain wavelength regions have long been described by the French word "etioler", meaning "to grow pale or weak". The possible confusion of growth responses of seedlings and of more fully developed plants, the degree to which more than one controlling photoresponsive system might be involved, and the extent to which photosynthesis enters make the term unsatisfactory except in a descriptive sense (WASSINK and STOLWIJK 1956). The German word "Längenwachstum" is explicit but more restricted in its meaning. The growth of seed plants in darkness contrasted with their growth in light has been the subject of many descriptions, studies, and reviews (DE ÜANDOLLE 1832, V. SACHS 1874, BATALIN 1871, DARWIN 1896, M.AcDOUGAL 1903, SCHÖNFELD 1914, PRIESTLEY 1926, BuRKHOLDER 1936, ABERG 1943, and FuNKE 1944). Many lower plants pass through their entire life cycles in darkness and instances of seed plants doing it are known. MAcDouGAL (1903) obtained four successive generations of corms from Arisaema triphyllum growing in darkness. Growth of Zea mays from seed to seed with sugar supplied through cut leaves was accomplished with a dim "safe light" (SPOEHR 1942). G. Melchers (ed.), Aussenfaktoren in Wachstum und Entwicklung © Springer-Verlag Berlin Heidelberg 1961
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H. A. BoRTHWICK and
S. B. HENDRICKS: Effects of radiation on growth and development.
Distinctive features of growth of monocotyledons and dicotyledons in darkness
