The natural history of plants, their forms, growth, reproduction, and distribution; . of the hard bast, the alterationproduced by the push and strain is only temporary, necessitates no interruptionof function, is perhaps even beneficial to the movement of the materials, and, whichis the main point, no rupturing and no permanent bending of the soft delicate-walled structures ensues. These delicate-walled elements, especially those of the soft bast, are protectedagainst harm from lateral pressure by the deposition of various tissues, especiallycork, in front of them (fig. 125^), which, like the
The natural history of plants, their forms, growth, reproduction, and distribution; . of the hard bast, the alterationproduced by the push and strain is only temporary, necessitates no interruptionof function, is perhaps even beneficial to the movement of the materials, and, whichis the main point, no rupturing and no permanent bending of the soft delicate-walled structures ensues. These delicate-walled elements, especially those of the soft bast, are protectedagainst harm from lateral pressure by the deposition of various tissues, especiallycork, in front of them (fig. 125^), which, like the buflfers of an engine, keep ofl, orconsiderably weaken, the lateral thrust and pressure. Remarkable contrivances for MECHANISMS FOR CONVEYANCE TO AND FRO. 475 protection against lateral pressure are also found in creepers and climbing plantswith perennial woody stems, and in those plants which are commonly called order to comprehend these contrivances rightly, it is necessary first to get anidea of the position of the parts requiring protection in perennial woody plants,. Fig. 127.—Rhynchosia phaseoloides, a Liane with ribbon-like Stems. which neither climb nor creep, and which possess an erect, straight, column-liketrunk. As previously stated, in these plants to which belong the firs, oaks, beeches,elms, limes, apple-trees, and, generally, the majority of leafy trees, the vascularbundles are arranged in a ring round the central pith, and consist essentiallyof the woody portion, serving to conduct the raw sap, and the bast portion, whichis employed in the transmission and transformations of the organic substancesformed in the green cells. These two portions are separated in the plants men- 476 MECHANISMS FOR CONVEYANCE TO AND FRO. tioned by a layer of tissue in which a very vigorous formation of new cells iscarried on, termed the caTnbium (fig. 125^). From this cambium, which appears asa ring in the circular cross section of erect stems, cells develop which on one s
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1902
