Text-book of structural and physiological botany . s,or by a single cell increasing from 20 to 50 times its original length. Thesimple consideration, however, that if the growth of bast-tubes wereof the latter nature, it must be accompanied by an increase in thicknessof the entire bundle of which it formed a part, which is not actually thecase, shows that they can arise only by the coalescence of cells. A close relationship subsists between sieve-tubes,vesicular vessels, and laticiferous vessels, partly on accountof their form, partly of their contents ; all appearing tohave for their function
Text-book of structural and physiological botany . s,or by a single cell increasing from 20 to 50 times its original length. Thesimple consideration, however, that if the growth of bast-tubes wereof the latter nature, it must be accompanied by an increase in thicknessof the entire bundle of which it formed a part, which is not actually thecase, shows that they can arise only by the coalescence of cells. A close relationship subsists between sieve-tubes,vesicular vessels, and laticiferous vessels, partly on accountof their form, partly of their contents ; all appearing tohave for their function the storing up of nutrient fluids,and the conducting of them to the parts of the plant wherethey are required. Sieve-ticbes or bast-vessels result from the coalescence ofcells standing one over another, the partition walls of which,or Steve-discs, have become perforated in the manner of a sieve ; TJic Cell as a Member of a Group, 49 and some have also sieve-like perforations through theirside-walls (Figs. 71-74). Of similar construction are lat-. FiG. 72.—Longitudinal section throughthe transverse partition-walls in thesieve-tubes of the gourd ; Z the pri-mary cellulose-wall ; h the second-ary cell-wall ; v v the peculiar thick-ening which is always found in youngcells ; i the contents contracted andpassing through the perforations inthe transverse partition-wall. Its Fig. 71.—Sieve-tubefrom the whitebryony, Bryoniadioica, the horizon-tal partition-wallswith peculiar thick-enings, (x 250.)
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