The fibrous tissue of wood deprived by certain solvents of several foreign matters which it contains was for long considered to be purely an element. Payen, as a result of important studies, showed that this substance, looked upon until that time as of a pure, woody nature, is only a mixture of different bodies,_ and that it results from the juxta position oi elongated cells containing in their interior a pure and amorphous matter, which is found in more or less regular layers. Each cell of the wood may be considered as being formed principally of an exterior substance (to which Payen gave the name cellulose) and of an incrustated matter the composition of which appears to be complex. The incrustated matter preponderates in hard wood: being very abundant in fruit-stones, it forms the stony concretions of certain pears. The elongated cells of the woody tissues enclose it in beds more or less thick. More abundant in the heart than in the sap-wood, it is often of a yellowish or brownish colour. Heavy and hard wood contains it in greater quantities than does white and light wood.