Detached leaves of Little Club wheat were allowed to senesce on water or on kinetin (10 mg/l.) in petri dishes on the laboratory bench. Samples taken at intervals of 24 to 48 hours for 8 to 10 days were fixed in permanganate or osmium tetroxide, embedded, usually in araldite or epon, and examined by electron microscopy. Abnormalities were noted in the endoplasmic reticulum (ER) of the mesophyll cells 2 days after the leaves were detached; ER and cytoplasmic ribosomes were not present after 4 or 5 days. Swelling of the mitochondria and degeneration of the cristae, collapse of the chloroplast grana, and abnormalities in nuclear structure were noted after 3 days. Vacuolar contraction occurred in some cells after 4 days but the plasma membrane usually remained unbroken until the seventh or eighth day, by which time the mitochondria were no longer recognizable and most of the chloroplasts and nuclei had also disintegrated.Kinetin induced an increase in the amount of ER and ribosomes and markedly delayed the degeneration of cellular fine structure.