A Blade Tissue Study of Leaves of Forty-Seven Species of Ficus

Abstract

Blade tissues (dermal, mesophyll, and vascular) of leaves, collected from plants growing in Southern Florida and greenhouses of the Missouri Botanical Garden, are descr. and compared. Most of the blades are elliptical to lanceolate in outline and range from thin meso-morphs to thick xeromorphs. Blade area ranges from 3.2 to 542 sq. cm.; blade thickness, from 66 to 573[mu]. Blade area and blade thickness are unrelated. The 11 mesomorphs have a single, well-developed epidermis and the usual contrast in spongy and palisade mesophyll. Leaves of 28 spp. possess a thin epidermis, a conspicuous hypoderm, compact palisade, and a large vol. of diffuse spongy mesophyll. The mean relative vols. for the 3 major nonvascular tissues are dermal (including epidermis and hypoderm), 26.7%; palisade, 38.7%; and sponge, 34.4%. The dermal layers are the most constant in relative vol.; palisade, intermediate; and spongy mesophyll, the most variable. Dermal vol. is closely correlated with blade thickness (r=0.9061). This study, along with others, suggests that all dermal elements function in the distr. of materials in the plane of the blade. The spacing of the minor veins, expressed as intervascular intervals, varies from 85 to 286u; vein length, from 53 to 171 cm. per sq. cm. These and other measures of vein spacing are compared and discussed. Leaves from the Florida outdoor plants are smaller, thicker, and have denser vein patterns than those from the greenhouses. For the 47 spp., a significant coefficient of correlation (0.8169) was observed between vein spacing and the tissue vol. ratio, (S+D)/P. The numerator of the ratio includes the laterally contiguous spongy mesophyll and dermal tissues; the denominator represents the laterally noncontiguous palisade. Larger vols. of dermal and spongy tissues are associated with the wider vein intervals while larger portions of palisade correspond with the denser vein patterns. This finding supports the idea that the final adjustments among the tissues during maturation are related to problems of water and solute translocation through the living cells of the blade. 32% of the total minor vein length is associated with bundle sheath extensions. The veins with extensions anastomose, isolating variously shaped units of chlorenchyma. In some leaves, the chlorenchyma is interrupted by variously branched intrusive veins (veins without extensions). Five distinct minor vein patterns are recognized.