质体外途径（英语：apoplast pathway）或质体外运输是相对于共质体途径的另一种无机盐运输方式，和共质体途径同为高等植物把水及无机盐从土壤运送到木质部的方法。

土壤中的水分和无机盐由根吸收之后，不输入细胞内，就沿着细胞壁中的空隙从表皮、皮层到内皮层，进入木质部。但是内皮层细胞壁中有不透水的凯氏带，会阻止水及离子的运送，因此到内皮层时，会又转为共质体途径，往细胞内部运送到木质部的导管。

Within a plant, the apoplast is the space outside the plasma membrane within which material can diffuse freely. It is interrupted by the Casparian strip in roots, by air spaces between plant cells and by the plant cuticle.

Structurally, the apoplast is formed by the continuum of cell walls of adjacent cells as well as the extracellular spaces, forming a tissue level compartment comparable to the symplast. The apoplastic route facilitates the transport of water and solutes across a tissue or organ. This process is known as apoplastic transport.