ANATOMY AND ULTRASTRUCTURE OF PITH FLECK-LIKE TISSUES IN SOME ROSACEAE TREE SPECIES

Unusual xylem tissues were found in Amelanchier laevis, Prunus pensylv anica, P. virginiana, Sorbus americana and S. aucuparia. These zones o f abnormal xylem were composed of hypertrophied cells and bands that a pparently comprised collapsed cells. The hypertrophied cells appeared to occupy gaps that began to form in the cambial zone. Histochemical t ests indicated that the bands were highly lignified and impermeable to an aqueous solution of KMnO4, as revealed by fluorescence. Transmissi on electron microscope examination disclosed clearly that the bands we re composed of collapsed cells and showed that the hypertrophied cells had thicker walls which contained, at times, additional layers. Altho ugh the cause of this tissue formation is unknown, its anatomy is quit e similar to pith fleck tissues reported by others as being caused by cambium mining insects.