On the basis of whether the first detectable product of CO2 fixation is a three or four-carbon compound, green plants are classified into C3 and C4 plants. In C3 plants, the first photosynthetic product is a three-carbon compound, the phosphoglycerate. Examples of C3 plants are beans and most of dicot plants. However, there are also many monocots, such as wheat, rice and oat, which are C3 plants. In C4 plants, the first photosynthetic product is a four carbon compound, the oxaloacetate. Most of tropical grasses are C4 plants. Typical examples are maize (Zea mays) and sugarcane (Saccharum officinale). There are also dicot plants which are C4 plants, e. g., Amaranthus sp. C3 and C4 plants differ from one another in their leaf anatomy. In contrast to C3 plants, the leaves of C4 plants are characterized by the Kranz anatomy in which the vascular bundles are surrounded by a concentric layer of bundle sheath and mesophyll cells. Normally, the chloroplasts of mesophyll cells habe well developed grana structure whereas grana structure is absent or poorly developed in the chloroplasts of bundle sheath cells. Bundle sheath chloroplast from larger number of starch grains than the chloroplast of mesophyll cells. This can be easily demonstrated by treating leaf sections with iodine solution which stains the starch grains.