A Textbook of Botany for Colleges and Universities; Ecology

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1911 Excerpt: ...twig of the cottonwood (Populus deltoides); note the large buds with imbricated scale leaves (c); note also that the lateral buds (c) are about as well developed as the terminal bud(/); other lettering as in 1057; 1059, a twig of Catalpa; note the small winter buds, both terminal (/) and lateral (c); note also the prominent circular leaf scars (/) with an inner circle (v), representing the position of the vascular bundles severed upon leaf fall. trolled in the main by definite external factors rather than by an influence residing in the main shoot. Elongation in spring may be associated with the vigorous movement of structural materials at that season, and subsequent dwarfing may be associated with a reduced movement, perhaps supplemented by increased desiccation. The amount of branch elongation varies with the season and is reciprocal to the width of the annual ring (p. 691), maximum elongation occurring in moist and minimum elongation in dry seasons. Differences between twigs of different species (e.g. the slender elongated twigs of willows, as compared with the stout twigs of the sumacs) appear inherent rather than related to external factors. Additional periodic phenomena.--Periodicity is exhibited in the daily growth of stems, elongation being greater by night than by day, as is illustrated by the bamboo, of whose extraordinary growth about two thirds occurs by night. The factors here involved are complex, but may be associated in part with the absence of light (directly or indirectly or both) and with lessened transpiration. Notable periodicity is exhibited by biennial rosette plants (fig. 1036), in which, possibly because of insufficient structural material, there is no stem development during the first season, though a vigorous erect stem rises in t...