山药在地下部形成块茎的同时,在地上部叶腋间常形成很多零余子。零余子是腋芽的变态,也即侧枝的变形,称为地上块茎,也叫气生块茎或株芽,俗称山药豆。零余子呈椭圆形,长1～2.5厘米,直径0.8～2厘米,褐色或深褐色,亩产量可达200～600公斤。一般情况下,零余子在山药茎蔓第20节以后发生,而且开始时多发生在山药主茎或侧枝 Yam formation in the underground tubers at the same time, often in the ground above the axillary axillary formation many. More than a child is axillary bud metamorphosis, that is, the deformation of the collateral, called the tubers on the ground, also known as air-born tubers or plant buds, commonly known as yam beans. More than a child oval-shaped, 1 to 2.5 cm long, 0.8 to 2 cm in diameter, brown or dark brown, mu yield up to 200 to 600 kg. Under normal circumstances, more than a child in the yam stem vine section 20 after the occurrence, and more often occurred in the yam main stem or side branches