Interveinal Distance for Carbohydrate Transport in Leaves of C3 and C4 Grasses1

Among common crop and range Gramineae, we found that species with the C4 pathway for photosynthesis had fewer cells between leaf vascular bundles than did C3 species. We extracted chlorophyll from leaf segments of 10 Ca and 10 C4 species, cleared the segments in 10% aqueous NaOH, counted the number of mesophyll cells between vascular bundle sheaths, and measured the distance (center to center) between the vascular bundles. The C3 species had 9 to 15 mesophyll cells between vascular bundle sheaths, while the C4 species had only 2. The vascular bundles were 0.18 to 0.36 mm (average 0.27) apart in C3 species, but only 0.08 to 0.15 mm (average 0.11) apart in C3 species. The closeness of all leaf cells to vascular tissue in C4 species suggests efficiency for transporting the products of photosynthesis and may be an important factor in their greater capacity to fix CO2.