Growth Correlations within the Segment in the Araceae

Abstract

The segment is defined as an internode and the associated petiole and lamina. In many climbing members of the family Araceae, there is great variation in the relative sizes and shapes of the three component parts of the segment. In Syngonium standleyanum Bunting, it was found that the form of the internode may be characterized by its length and diam, the petiole by its length, and the lamina by its wt and its shape (the ratio of central lobe wt to lamina wt). The sizes and shapes of the various components of the segment were found not to be allometrically related, with three exceptions: the internode diam is allometrically related to the segment wt, petiole wt, and lamina shape. In the four species of Araceae studied, the strong correlation between the diam of the internode and the wt of the entire segment results in a trade-off between making a large leaf or a long internode. For an internode of a given diam, the total dry wt of the segment is fixed, but may be proportioned in virtually any manner between the leaf and internode, from 95% of the wt in a large leaf, to 98% of the wt in a long internode. The complete form of the segment may be defined by just two variables. A suitable pair of variables is internode diam, and the ratio of internode diam to internode length.