Leaf blades of forty-seven species of Ficus were studied. Approximately half of these were collected in southern Florida; the other half from greenhouses at the Missouri Botanical Garden. 2. The sampling included thin mesomorphs and thick xeromorphs; most of the blades are elliptic or lanceolate in outline. 3. Blade area ranges from 3.2 to 542 sq. cm. (mean, 106 sq. cm.); blade thickness ranges from 66 to 573 μ (mean, 216 μ). Blade area and blade thickness are unrelated. 4. The blades of the eleven mesomorphs have a single, well-developed epidermis and the usual contrast in laterally contiguous spongy mesophyll and noncontiguous vertical palisade. Eight leaves of intermediate thickness show an occasional doubling of the epidermis. Some of these have a compact all-palisade mesophyll, but portions of the "palisade" cells were found to be laterally connected. Leaves of the largest group, twenty-eight species, possess a relatively thin epidermis, a conspicuous hypoderm, compact palisade, and a large volume of diffuse spongy mesophyll. 5. The volumes of the three major nonvascular tissues were measured. Of the three, the dermal tissue (whether composed of a single epidermis or of epidermis and hypoderm) is the most constant in relative volume. In all leaves it occupies approximately one-fourth of the total blade volume. 6. Palisade varies in volume from leaf to leaf and from a single layer to multiple layers; it is relatively compact in all leaves. Its cells are relatively uniform in size and show limited lateral contact. Although the spongy mesophyll is highly variable in density and volume, it always consists of cells which are contiguous in the lateral plane. Spongy mesophyll cells are highly variable in size and shape, but the diameter of their "conjugating" arms is uniform and comparable with the diameter of palisade cells. 7. Dermal volume is closely correlated with total blade volume (r = 0.9061). This probably means that the function of hypoderm and other internal dermal elements is similar to that of the epidermis itself. All dermal elements probably function in the distribution of materials in the plane of the blade. 8. A significant correlation (r = 0.8169) was observed between vein spacing (IVI) and the volume ratios of the laterally contiguous spongy mesophyll and dermal tissues to the laterally non-contiguous palisade, (S + D)/P; that is, large portions of dermal and spongy tissue are associated with wide vein intervals, and comparatively large portions of palisade correspond with denser vein patterns. These findings support the idea that the final adjustments of tissues during maturation are related to problems of water and solute distribution from veins through nonvascular tissues. In all probability the dermal tissue and spongy mesophyll function in the lateral distribution of materials across the blade. The fact that the portion S/P of the ratio (S + D)/P is also closely correlated with vein spacing (r = 0.7907) shows that the sponge and palisade may be the tissues most closely associated with vein spacing. 9. The veins are arranged in various complex patterns. Of the total veins 32% have bundle-sheath extensions. In general the veins with extensions anastomose, isolating polygonal blocks of chlorenchyma. These blocks may or may not be invaded by branched veins carrying no extensions. Five types of vein patterns were recognized. Intervascular intervals ranged from 85 μ to 286 μ; the mean, 155 μ. Intervals between veins carrying bundle-sheath extensions range from 223 μ to 9010 μ. Extremes in vein length are 52.8 and 170.5 cm/sq cm, the mean, 98 cm/sq cm. Two indices for measuring vascularization (intervascular interval and vein length) were found to be fairly comparable (r = -0.8938). The intervascular interval, however, was more closely correlated with (S + D)/P and was thus considered to be the more accurate index of the two. 10. The leaves from the Florida outdoor plants are smaller and thicker than are those from the greenhouse. The Florida leaves have a relatively low mean S + D/P ratio, 1.44, as compared with 1.92 for the greenhouse leaves. Dense vein patterns are associated with the lower tissue ratios of the Florida leaves. The coefficient of correlation for (S + D)/P and IVI is significantly higher for the outdoor leaves (0.8593) than for the indoor samples (0.7481).
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Jane Philpott (1953) studied this question.