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ARRACACIA XANTORRHIZA: EL TUBERCULO COMESTIBLE DEL APIO CRIOLLO Y SU ESTRUCTURA INTERNA

INGRID ROTH
Acta Botánica Venezuélica
Vol. 12, No. 1/4 (1977), pp. 147-170
Stable URL: http://www.jstor.org/stable/41740667
Page Count: 24
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
ARRACACIA XANTORRHIZA: EL TUBERCULO COMESTIBLE DEL APIO CRIOLLO Y SU ESTRUCTURA INTERNA
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Abstract

El tubérculo radical se distingue de la raíz filamentosa sobre todo por su abundante crecimiento en anchura. El xilema sufre una modificación en cuanto se forman pocos vasos, pero mucho parénquima rico en almidón. Puesto que el xilema se diferencia poco, se conserva la ordenación de las células en hileras radiales. El floema funcional es mínimo en el tubérculo y ia distinción entre parénquima floemático regular y parénquima amilífero se pierde en etapas avanzadas, puesto que casi todas las células parenquimáticas se llenan de almidón; este último es del tipo compuesto. El sabor viene de las gotas de aceite etérico que se encuentran en casi todas las células parenquimáticas, pero sobre todo en las células secretoras y en los canales secretores que se forman dentro del parénquima amilífero; este último es del tipo aliforme confluente —con respecto a la manera de rodear los canales— y forma junto con los radios medulares una red de parénquima rico en almidón, visto en corte transversal. Los canales secretores se originan de manera esquizogénea. El corcho se desarrolla en forma de "pisos" ("Etagen-kork") en céulas superpuestas que se dividen periclinalmente; de esta manera puede adaptarse al crecimiento de dilatación; se encuentra este tipo de corcho habitualmente en monocotiledóneas. El tubérculo se hace entonces comestible por la abundancia de parénquima con paredes delgadas, tanto en el xilema como en el floema, y la ausencia casi completa de tejido mecánico. Las sustancias nutritivas del tubérculo son sobre todo el almidón y, en cantidad mucho menor, el aceite. The tuberous root is distinguished from the filamentous one principally by its growth in thickness. The xylem suffers a modication in so far as only few vessels form, but a high quantity of parenchyma, rich in starch. As the xylem differentiates little, the cell arrangement in the form of radial rows is maintained. The functional phloem remains very small and the distinction between regular phloem parenchyma and amyliferous parenchyma is lost in more advanced stages, as almost all parenchyma cells become filled with starch; this is of the compound type. The special flavour comes from the eteric oil in the form of small droplets which are found in almost all parenchyma cells, but first of all in the secretory cells and canals which develop within the amyliforous parenchyma; the latter surrounds the canals in a "aliform-confluent" way and, together with the medullary rays, forms a network of starchy cells, as seen in transverse section. The secretory canals originate schizogeneously as intercellular spaces in the center of (3 to) 4 cells. The cork develops in the form of stories in superposed cells which divide repeatedly periclinally; in this way, the cork is able to adapt to growth in circumference; this type of cork is otherwise characteristic of monocotyledones. The tubercle becomes edible through the development of high quantities of parenchyma with delicate walls which forms in the xylem as well as in the phloem, and by the almost complete absence of strong mechanic tissue. The nutritive substances of the tubercle are first of all starch and, in a much more reduced quantity, also oil.

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