One hypothesis advanced to explain the first type of sensing mechanis involves differential carbon assimilation patterns of mesophyll cells on either side of major veins due to microtopographical shading effects.

• 由于主脉两侧叶肉细胞的荫影效应，导致了碳同化的差异，这个假设可以解释前面的第一种类型的感受机制。