Regulation of the Cataphyll-Foliage Leaf Transition
A particularly striking pattern of development exhibited by perennial plants is the periodic alternations in the production of cataphylls (bud scales) and foliage leaves during the formation of the resting bud. In general, cataphylls are initiated by the shoot apex early in the spring starting at about the time the bud is expanding. After producing the cataphyll number characteristic of the species, the shoot apex initiates the production of foliage leaves. Leaf production continues until all, or a large part, of the succeeding years leaves are formed. Previous studies of this phenomenon have dealt largely with the morphological development of these lateral appendages and speculated on the morphological nature of the cataphyll (Cross, 1936, 1937, 1938; Foster, 1929, 1931, 1932, 1935, 1937; Sterling, 1947; Sacher, 1955). With the exception of a few recent studies (Steeves and Wetmore, 1953; Al-Talib, 1957; Sussex, 1958; Al-Talib and Torrey, 1961; Rouffa, 1967) a consideration of the casual factors regulating this type of heterophylly has been neglected. Numerous experimental studies have been directed to the problem of the regulation of dormancy however, and investigations of the photoperiodic responses of woody perennials have shown that the formation of the resting bud, hence the initiation of cataphyll production, is day-length sensitive (Wareing, 1956; Nitach, 1956). The goal of the present study is 1) to determine the timing of cataphyll and foliage leaf initiation with particular reference to the transition from cataphyll to foliage leaf production in the developing bud, 2) to study and compare the development of cataphyll and foliage leaf primordia for similarities and differences and 3) to determine the casual factors regulating the development of primordia as cataphylls or foliage leaves.