On the phloem of Mimosa pudica L
1970
Esau, K.
The phloem of Mimosa pudica L. was examined in view of some reports that the sieve elements in this plant show features not previously described for these cells in Leguminosae. In the present study only a usual dicotyledonous type of sieve element was recognized. The sieve elements pass through stages of differentiation involving development and dispersal of P-protein bodies, disintegration of nuclei, and appearance of plastids storing a starch staining red with iodine. Callose occurs on the transverse or moderately oblique sieve plates. The phloem contains secretory cells. They are wide and long and have transverse or more or less inclined end walls. In younger cells the end wall bears in the centre a conspicuous pit to which the protoplasts of the superimposed cells are firmly attached. In many older cells the pit region is replaced by a perforation so that the contents of superimposed cells may be completely merged. It remains to be determined whether the perforation is present in an intact plant or results from a rupture during sampling. The secretory cells accumulate material that gives a positive test for carbohydrates and a negative test for proteins.
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