These then would seem to be the differences in the parts which make up the plant. Those which belong to the qualities^[1] and properties are such as hardness or softness, toughness or brittleness, closeness or openness of texture, lightness or heaviness, and the like. For willow-wood is light from the first, even when it is green, and so is that of the cork-oak; but box and ebony are not light even when dried. Some woods again can be split,^[2] such ​as that of the silver-fir, while others are rather breakable,^[3] such as the wood of the olive. Again some are without knots,^[4] as the stems of elder, others have knots, as those of fir and silver-fir.

Now such differences also must be ascribed to the essential character of the plant: for the reason why the wood of silver-fir is easily split is that the grain is straight, while the reason why olive-wood is easily broken^[5] is that it is crooked and hard. Lime wood and some other woods on the other hand are easily bent because their sap is viscid.^[6] Boxwood and ebony are heavy because the grain is close, and oak because it contains mineral matter.^[7] In like manner the other peculiarities too can in some way be referred to the essential character.