. A textbook of botany for colleges and universities ... Botany. STEMS 733 as elsewhere, the destruction of the terminal shoot is followed by the development of many lateral branches, whose subsequent destruction results in a still greater number of new laterals, and so on, until there is at last an inextricable tangle of branches. The tortuous descending branches so characteristic of alpine conifers probably are associated with severe mechanical factors, such as strong winds, the weight of the winter snow, and snowslides. Even below the " timber line," tree trunks sometimes bend dow
. A textbook of botany for colleges and universities ... Botany. STEMS 733 as elsewhere, the destruction of the terminal shoot is followed by the development of many lateral branches, whose subsequent destruction results in a still greater number of new laterals, and so on, until there is at last an inextricable tangle of branches. The tortuous descending branches so characteristic of alpine conifers probably are associated with severe mechanical factors, such as strong winds, the weight of the winter snow, and snowslides. Even below the " timber line," tree trunks sometimes bend down-hill at the base, owing to the weight of snow borne by the plant when it was a young and flexible sapling. Arctic dwarfs.—The polar regions, like the mountain tops, are characterized by dwarf vege- tation, composed largely of cushion herbs, rosette herbs, mat-forming plants, and Krumm- holz. The Krummholz is made up largely of dwarfed specimens of woody plants { larch, spruce, and birch) which in more genial climates develop into trees. While not experimentally attested, it is likely that the factors involved are similar to those that are supposed to obtain on mountains; transpiration, perhaps, is less than in alpine regions, on account of the less intense light and the greater atmospheric pres- sure, but absorption also is less, because the soil is more constantly cold. Dwarfing in arid situations. — Xerophytic vegetation, such as that of dry rocks and sand, often is dwarf, though much less so than that of alpine and arctic regions, and the dwarfness is less clearly due to the surrounding conditions. The stem of Equisetum hyemale, which com- monly is unbranched in mesophytic and swampy habitats, often is much branched in dry, exposed situations, the destruction of the terminal shoot by excessive transpiration or otherwise being followed by a strong development of lateral branches, as in the Krummholz ( 1054, 1055). The mesquit (Prosopis juliflora), which is a t
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
