GROWTH RELATIONSHIPS OF LEAVES AND INTERNODES IN VINY ANGIOSPERMS WITH DIFFERENT MODES OF ATTACHMENT

The timing of leaf expansion in relation to the elongation of adjacent internodes was compared in 37 species of vines which climb by means of twining stems, tendrils, or roots. Interspecific comparisons were made with a growth index, L, defined as the fraction of the final length of a leaf when an adjacent internode reached 75 % of its final length. The index was calculated for both of the leaf positions adjacent to an internode: La for the leaf above the internode, Lb for the leaf below the internode. The value of L was low in many twiners and tendril climbers (La, Lb < 0.33 in 15 of 29 species). Four twiners formed scale leaves (La and Lb = 1.0) and in two climbers with leaf tip tendrills (Pisum, Gloriosa) the maturation of leaves was not delayed (La = 0.73, 0.94 respectively). In all five species (5/5) of monocotyledonous root climbers a leaf completed elongation together with, or before, one of the adjacent internodes. In 2/3 species of dicotyledonous root climbers the elongation of leaves was delayed in relation to both adjacent internodes, but the value of La was greater than in most twiners. The timing of adjacent internode elongation was evaluated using a second index, T, defined as the fraction of final length of an internode when the subjacent internode reached 75 % of its final length. Wide-ranging extremes were found among various species, from 0.70 in Asparagus to 0.05 in Anthurium. Root climbers exhibited generally lower T values than twiners or tendril climbers. These results are in agreement with the concept of earlier qualitative studies that the pattern of leaf and internode development in vines is related to their mode of attachment. Delayed leaf expansion has been considered important in the biology of twining and tendril climbing vines because large foliage leaves are thought to decrease the effectiveness of shoots "searching" for a support. The present study provides the first quantitative, comparative description of the timing of leaf growth in vines. The leaves of non-vines commonly mature together with, or before, the adjacent internodes. VARIOUS AUTHORS have described the expansion of foliage leaves in the shoots of twining and tendril-climbing vines as delayed behind the elongation of internodes (Schenck, 1892; Raciborski, 1900; Gradmann, 1929; Troll, 1937; Baillaud, 1962). The timing of leaf expansion in root climbers has not received much attention. One goal of this study is to describe in detail the growth relationships between leaves and internodes of vines, according to their mode of attachment. Previous accounts have dealt only with the relative size of leaves along the shoot. A developmental index of leaf expansion will be selected to make quantitative comparisons among vines, as well as comparisons with the literature on leaf expansion in non-vmes. Shoot extension is pronounced in many vines, and for this reason they are especially suitable for studies of internode development. Very little information is available about the timing of the elon1 Received for publication 8 April 1976; revision accepted 7 October 1976. This study was supported by NSF Grants GB-40065 and BMS73-01226. I thank Jack B. Fisher for many useful discussions, and Mary French and Jan Wassmer for patient help with measurements. gation of successive internodes (Wetmore and Garrison, 1966). A second goal of the study is to describe this aspect of internode development using a quantitative index, and to integrate the results with previous descriptions of the growth of individual internodes of vines (Fisher and French, 1976; French and Fisher, 1977). Both monocotyledonous and dicotyledonous vines have been included in this study so that taxonomic comparisons of leaf and internode development can be made. Recent comparisons of viny shoot growth in angiosperms, which have been published without supporting documentation, (Stebbins, 1974) may now be appraised. MATERIALS AND METHODS-Plants under cultivation in greenhouses or in outdoor plantings at Fairchild Tropical Garden, or the USDA's Subtropical Horticulture Research Unit, Miami, Florida, were measured during the periods given for each species (Table 1). Both the maximum and minimum temperatures during the study period, and the average daily temperature at Miami International Airport, approximately 7 km to the north, are also included in Table 1. Temperature data were obtained from the National Oceanic and