Abstract:
Botanists at the close of the nineteenth century believed that the ontogeny of leaf shape in individuals recapitulated the phylogeny of leaf shape in the taxonomic groups to which the individuals belonged. At the Start of the twentieth century these ideas were abandoned leaving no satisfactory hypothesis as to the reason for variation in leaf shape either from plant to plant or within the same plant. Sinnott (1935) considered that two types of genes were involved: those controlling size, and those controlling relative growth rates thus producing shape or patterns. He states that whether they produce their effects by a control of growth localization, cell polarity, or other mechanisms are questions about which almost nothing is known. The influence of these genes is evident in the very early developmental stages and clearly controls the entire growth plan through which the organ passes in its development. Certain basic rates may be determined by "size genes" and thus influence total growth directly. Development however involves a series of correlated growth rates and it is this correlation in growth resulting in specific organic forms with which the genes for shape are evidently concerned.
