LEAF PARENCHYMA WITH TRANSFER CELL-LIKE CHARACTERISTICS IN THE MOSS,POLYTRICHUM COMMUNE HEDW

Mature leaves of Polytrichum commune Hedw. were examined in regard to structural features and possible solute transport mechanisms. The leaf bundle is organized into several parenchyma layers which are termed passage cells, deuters, and socci. The deuters (leptoids of some authors) are large-diametered parenchymatic elements which exhibit papillate wall ingrowths characteristic of transfer cells. The deuter cytoplasm is typical of transfer cells, including a large number of mitochondria, numerous polysomes, and a peripheral network of ER associated with the wall ingrowths. Deuters show little ultrastructural similarity to leptoids (sieve elements of bryophytes) of the stem. Socci parenchyma and passage cells have a distinct inner wall layer which is convoluted in places, and therefore, these cells as well as the deuters might be involved in intensive short-distance fluxes of solutes. A possible translocation mechanism involving an active, carrier-mediated loading of leaf parenchyma is discussed in relation to these structural features.