How crops growA treatise on the chemical composition, structure, and life of the plant, for all students of agriculture .. . NS OF PLANTS. 281 a. the sieve-cells in the overground stem of the potato; A,-B, cross-section of parts of vascular bundle—-4, exteriorpart towards rind; ^, interior portion next to pith—a, a,cell-tissue inclosing a the smaller sieve-cells, A, JB, which «contain sap turbidwith minute gran- _ules; b, cambiumcells; c, wood-cells(which are absent inthe potato tuber;) d, ^ducts intermingledwith wood-cells. Orepresents a sectionlengthwise of thesieve-ducts; and D,more highly
How crops growA treatise on the chemical composition, structure, and life of the plant, for all students of agriculture .. . NS OF PLANTS. 281 a. the sieve-cells in the overground stem of the potato; A,-B, cross-section of parts of vascular bundle—-4, exteriorpart towards rind; ^, interior portion next to pith—a, a,cell-tissue inclosing a the smaller sieve-cells, A, JB, which «contain sap turbidwith minute gran- _ules; b, cambiumcells; c, wood-cells(which are absent inthe potato tuber;) d, ^ducts intermingledwith wood-cells. Orepresents a sectionlengthwise of thesieve-ducts; and D,more highly magni-fied,exhibits the fine-ly perforated, trans- dverse partitions,through which theliqidd contents free-ly pass. Milk Ducts.—Be- asides the ducts al-ready described,there is, in manyplants, a system ofirregularly branchedchannels containing ^ -^S- 55. a milky juice, as in the sweet potato, dandelion, milk-weed, etc. These milk-ducts, together with many otherdetails of stem-structure, are imperfectly understood, andrequire no further notice in this treatise. HerbaceOHS StemS>—Annual stems of the exogenous. 282 HOW CEOPS GROW. kind, whose growth is entirely arrested hy winter, consistusually of a single ring of woody tissue with interiorpith and surrounding bark. Often, however, the zone ofwood is thin, and possesses but little solidity, while thechief part of the stem is made up of cell-tissue, so that thestem is herbaceous. Woody StcmSi—^Perennial exogenous stems consist, intemperate climates, of a series of rings or zones, corre-sponding in number Avith that of the years during whichtheir growth has been progressing. The stems of ourshrubs and trees, especially after the first few years ofgrowth, consist, for the most part, of woody tissue, the pro-portion of cell-tissue being very small. The annual cessation of growth which occurs at theapproach of winter, is marked by the formation of smalleror finer wood-cells, as shown in fig. 54, while the vigorousrenewal
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectagricul, bookyear1868
