Plant tissue cultures exhibit in the majority of cases a diversity of cell types. This may be caused either by the complexity of the explanted material or by its potencies. Only in a few cases tissue cultures have been obtained consisting of one type of cells. These cultures were derived from cambium. For the experimental approach of the problem of plant cell differentiation these simple tissue cultures may prove to be important. It is conceivable that a simple tissue might breed true. This consideration and the fact that it differentiates very early in stem development led us to choose pith parenchyma as a starting material. It might have lost some of its potencies and have become more or less physiologically and morphologically fixed as seems to be the case with some types of idioblasts. This, however, proved not to be the case. It is our intention to discuss the results obtained with the plants investigated in a series of short papers. They will concern Helianthus tuberosus L. Sambucus nigra L. var. pendula Dipp., Zinnia elegans Jacq., Ginkgo biloba L. and the variety aurea Carr, of Taxus baccata L.