Sieve Element of Impatiens Sultanii

Abstract

The sieve elements arise from vacuolate cells, and enlargement of one or more slime bodies increases the volume of cytoplasm relative to that of the vacuole. The slime finally disperses throughout the region once occupied by the vacuole. A new term, mictoplasm, is proposed for the resulting mixture of non-membranous cytoplasmic material, including slime, with the contents of the vacuole. The nucleus disappears during development, but before losing its chromaticity, it apparently releases one or more nucleoli into the cytoplasm. The extruded nucleoli are prominent during development but usually disappear with the tonoplast, nucleus, and dictyosomes as the cell matures. At maturity, small vesicles, plastids containing spherical starch grains, and sparsely distributed mitochondria deficient in tubules are attached to the plasmalemma. The sieve-plate connecting strand develops in a pore site bearing a pair of callose platelets and penetrated in the centre by a plasmodesms. The callose cylinder which surrounds the mature connecting strand is followed so that the shape of a connecting strand in cross section is stellate. Mictoplasm and the plasmalemma are continuous from one cell to the next through the sieve-plate connecting strands.