The Morphogenesis of Apple Buds

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Abstract
The early stages in the change from vegetative to reproductive development of apple spur terminal buds were followed by dissection of buds from untreated trees, and from trees defoliated at different times in the season. A change in the development of the leaf primordia occurred when there were approximately eight in the bud. This was followed by the development of bracts, which appeared to be necessary for the formation of actual flower parts. Leaf primordia tend to inhibit this process. Whereas their effect upon the apical meristem was subsequently reduced by the formation of bracts, so that eventually a terminal flower formed, their effect upon the lower lateral meristems was unaltered. These meristems therefore remained in a vegetative state. In addition to the number of leaf primordia in the bud, the degree of dormancy may be an important factor in determining the onset of flowering. Since the number of leaf primordia in vegetative buds at the end of the season is eight, the spatial distribution of primordia on the main axis of the bud and their vascular connexions might have a decisive effect on bud development. This was related to the effect of older primordia in the bud upon the development of younger ones. In buds in which these older primordia were inhibited by foliage, etc., i.e. those with a long plastochrone, no effects were observed upon the development of younger primordia and the buds remained vegetative. Whilst correlative inhibition of buds thus affected their ability to form flowers, there is no evidence of a critical leaf area for flowering. Flowering in apple buds is more likely to be due to the removal of factors inhibiting reproductive development than to the synthesis of a specific flower inducing substance as such.

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