The Role of Various Regions of the Bean Hypocotyl on Red Light-induced Hook Opening.

Measurement of various zones on the concave half of etiolated Phaseolus vulgaris L. (cv. Black Valentine) hypocotyls has shown that growth at the basal portion of the elbow and the contiguous upper portion of the shank was stimulated earliest by red light. Growth of these two zones was unaffected by the tissue of the convex half but was inhibited by tissue distal to them. The inhibition was alleviated by the continuous presence of shank tissue below the growing zones. Based on cuts made halfway through the hypocotyl at positions above, below, or between the two zones of growth, it is suggested that cells at the inner portion of the upper shank control in some way the light-induced growth of the elbow cells directly above.