Comparative Anatomy of Leaf of Cycads, with Reference to Cycadofilicales

Abstract

1. The similarity in the structure of the cortical armor of the petioles in the Cycadophyta and the Cycadofilicales furnishes additional indication of the affinity between these groups. 2 The structural features of the petiole in the Cycadophyta resemble the Medulloseae rather than the Lyginodendreae, thus giving evidence of a closer connection with the former than the latter group. 3. The structural features of the petiole in the Zamieae resemble the Medulloseae more closely than do the homologous structures in the Cycadeae, a situation which would indicate a more primitive position for the former suborder. 4. In the possession of many veined leaves, the Zamieae resemble more closely the ancient group than do the Cycadeae, and therefore would seem to be the more primitive of the two suborders. 5. The paleobotanical evidence at present available indicates that the many veined type of leaf was of earlier occurrence among the Cycadophyta than the type with a reduced number of veins. 6. The more simple structure of the female reproductive axis in the Cycadeae has been adduced as an argument in favor of the more primitive position of this suborder, but there is no sound evidence which would indicate that this structure is a primitive one rather than a reduction. This situation renders such evidence as to the primitiveness of the Cycadeae of doubtful value.