Chambers's encyclopaedia; a dictionary of universal knowledge . rom rudiments whichdevelop in an internal layer known as the stem has a persistent tendency to grow up-wards, while the root seeks the centre of the eartli,and in regard to other forces than that of gravity,stem and r<x)t usually behave in opposite ways (., Movements ok). In describing aerial stems we distinguish thenodes from which the leaves arise from the inter-vening internodes, the hiids which appear in theaxils of leaves from that which forms ihi apex, orfrom those which apjiear arbilrarily or adve
Chambers's encyclopaedia; a dictionary of universal knowledge . rom rudiments whichdevelop in an internal layer known as the stem has a persistent tendency to grow up-wards, while the root seeks the centre of the eartli,and in regard to other forces than that of gravity,stem and r<x)t usually behave in opposite ways (., Movements ok). In describing aerial stems we distinguish thenodes from which the leaves arise from the inter-vening internodes, the hiids which appear in theaxils of leaves from that which forms ihi apex, orfrom those which apjiear arbilrarily or adven-titiously, the leaf-bearing blanches from the llower-stalks, and so on. The branching of the stem isusually lateral, but there are divergent forms, suchas false dichotomy in the mistletoe, false axis inthe vine, or true dichotomv in some Lycopods (seeBkanch). In order to present a clear picture of the internalstructure of a stem, it will be convcnieni lo restrictour attenti(m in the first place to the young twigsof some Dicotyledonous tree, such as the Fig. 1.—Diagrammatic cross sections of a youngDicotyledonous Stem:A, ft two-year old stem; B. a llirtC-year old stem : a, pith; h,primary medullary rays ; c, wood, in two layers in A, in tlireelayers in B ; rf, cambium ring; e, bast: / cambium (interfas-cicular) between the bundles ; g, secondary medullary rays. Every one knows that it is easy to peel off thebark and to leave the white wood bare. This ispossible because the region known as the bark isseparated from the internal wood by a cylinder ofdelicate, readily rnjitured, actively dividing cells—the cambium. ^^hcn a ring of hark is cut oilatree, the leaves do not wither: therefore we con-clude that the water which friuu the roots)) up by the wood. But if in the ringingthe young wood be also cut, the leaves witherrapidly ; therefore it is by the young wood that thewater —a conclusion corroboraled by thefact that a tree may llouiish well al
Size: 2173px × 1150px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublisherlondo, bookyear1901
