we Demy- 4 gimme yd test ma a eae bay arp FRR AECD-3446 (App. ) 7 ‘eross-section of the normal mature stem of Ipomoea tuba just below the rue leaf shows a phellogen producing a thin-walled phellem several cells }. on the periphery. Progressing toward the center of the stem from this xe RE ted the collenchyma, four or ‘tive cells in depth; considerable assimi- ge & iF parenchyma containing lactiferous ducts and secretory cells; a uniseriay which may be an endodermis, but cannot be strictly identified as such Eyd acks Casparian strips and is not a starch sheaths a pericycle; external Broups; the cambium, several cells in thickness; a ring of secondary reversed by pith rays; radial rows of primary xylem; and a central pith Sning lactiferous ducts and strands of internal phloem (Figure 6). lj Both ‘and external phloem contain well developed sieve tubes and companion ‘he cortex and central parenchyma contain abundant starch and there are — gluster crystals. Bands of fibers occur in the xylem of the older stem. rportions of the stem are much the seme as to tissues and organization, that there are no xylem fibers and no phellogen, the stem being covered uniseriate epidermis. h longitudinal section of the normal primordium shows a uniseriate tunica ; the central, homogeneous corpus. Just back of the corpus region is of cell elongation and pronounced procambial development. Phloem is dif- The origins of lectiferous ducts in «the central and cortical regions may be distinguished at about the same L and many of the parenchyma cells contain large cluster crystals (Figure 7). The tumors consist largely of parenchymatous tissue with relatively small t would seem, inadequate amounts of xylem and phloem. The parenchyma cells ebout the same size as those ocourring in the central pith of the normal Ie. The xylem and phloem cells, on the other hand, are extremely small and re is apparently no cambial activity. The phloem varies from almost com _@ UNIVERSITY 4neiregy 'UNTY, OF WAih blo at 2 Ms ads PA ized one to two mmo back of the apex. err hey Ap It to distinguish in the longitudinal section, but xylem elements are easily