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Abstract
Uniform, actively growing apple seedlings, 10-15 cm high, were sprayed with 1000 ppm succinamic acid 2-2 dimethyl hydrazide (Alar). The apical portion of treated and control seedlings was collected at the following intervals after treatment: 3, 27 hr; 3, 6, 8, 14 days; 5 weeks. Sections through the apex were prepared, stained and examined microscopically for mitotic figures. As compared with controls, the frequency of mitotic figures in the stem apex of treated plants progressively decreased through 3 days, thereafter the number of figures increased to 69% of that in untreated plants on the 14th day. In the rib meristem frequency of mitosis declined slightly at 3 hr, then progressively until the 3rd day, after which the number of figures increased progressively to the 14th day when it was 28% of that in untreated plants. Only a temporary decrease in mitotic activity occurred in young leaf primordia during the first 6 days. Five weeks old treated seedlings were examined for histological abnormalities associated with extreme shortening of internodes.
Abstract
On current season’s growth of sour cherry (Prunus cerasus, cv. Montmorency) injury induced by (2-chloroethyl)phosphonic acid (ethephon) occurred at and below the nodes in tissues adjacent to the 3 leaf traces supplying each leaf. In the secondary xylem close to the cambium, separation and breakdown of cell walls resulted in the formation of gum cavities; injury occurred also in cortical tissues adjacent to the leaf traces. In older portions of the branch more severe injury occurred where large gum cavities formed in the outer secondary xylem and in cortical tissues. Superficial swelling, cell proliferation and surface cracks occurred on the branches near the nodes accompanied by exudations of gum. Injury and cell wall dissolution may be related to cellulase activity stimulated by ethylene released from the break down of ethephon within the tissues.