Frederic T. Lewis

The Development of Pinnate Leaves

Certain features of leaf development which were established some fifty years ago, should not be overlooked. These are primarily the basipetal and basifugal types of growth, which may be verified by collecting mature leaves, and which can profitably be taught to students of elementary botany. Among the basipetal leaves of the earlier writers there are two radically different types, represented by the rose and blackberry respectively. The rose should be separated from this class and its leaf development may be described as stipular. Mature leaves indicate that the rose stipules are formed before the lateral leaflets, as observed by Trecul and Lubbock but denied by Eichler. The formation of relatively simple leaves in plants which bear lobed or compound forms may be described embryologically, as an arrest of development in the primordial leaf followed by a stage of expansion, or by expansion before the embryological stage has been completed. Rapidity of growth may account for the constant location of the simpler leaves near the cotyledons, bud scales and sepals.