Sentence:  The process of "layering" is well known: it consists in bending a young branch ... into the soil to a certain depth, and elevating the top part of it out of the soil in an upright direction; in time the buried part takes root, and the shoot becomes a perfect plant. The root which produces the young shoots for layering is called the <WSD>stool</WSD>. <WSD>Stools</WSD> are planted about six feet apart every way in a deep fresh soil. ... <WSD>"Stool</WSD>". – The root of a tree which has been left in the ground, the produce of another tree, or shoot for saplings, underwood, &c. 
Meaning of the word marked with <WSD> tags:  A plant from which layers are propagated by bending its branches into the soil.