_Straw._—Straw pulp very closely resembles esparto-pulp in its microscopical features. The hairs above alluded to are, however, absent. On the other hand, a number of flat oval cells are always present in paper made from straw (_b_, Fig. 13). It should be borne in mind, however, that bamboo and similar pulps also contain these cells. _Wood (Chemical)._—Flat riband-like fibres, showing unbroken ends (see photographs, Frontispiece). The presence of the pitted vessels (Frontispiece, and _a_, Fig. 15) is eminently characteristic of pulp prepared from pine-wood. The fibres of other woods are not sufficiently characteristic. They much resemble those of pine-wood, with this difference, that the pitted vessels are absent. _Wood (Mechanical)._—Mechanical wood-pulp may be recognised by the peculiar configuration of the torn ends of the fibres, and from the fact that the fibres are rarely separated, but are generally more or less agglomerated (see Frontispiece). Pulp from pine of course shows the pitted vessels already referred to. They are usually more distinct than in chemical wood-pulp. Occasionally fragments are to be met with connected together with portions of the medullary rays. The microscopical examination of a paper is a matter of very great difficulty, and one requiring much practice. The student is recommended to study closely for himself the microscopical features of pulps obtained from authentic specimens. Some approximate idea of the relative proportion of the various fibres present in a paper can be obtained from a careful microscopical examination. Vétillart maintains that a quantitative determination within a fair limit of accuracy is possible. On the other hand, the {201} Berlin Prüfungsanstalt do not profess to do more than merely identify the fibres. In examining a paper under the microscope, it should be observed whether the fibres appear as fragments, or whether they consist of whole bast cells in which the tapered ends appear. Cotton and linen, owing to the great length of their ultimate fibres, yield, when beaten, fragments showing where the fracture has taken place. From the appearance of this fracture it is possible to ascertain whether or not the beating operation has been properly conducted. If the beater-knives have been too sharp, or have been let down to the bed-plate too quickly, the fractures will appear as clean cuts, whereas when the operation has been properly conducted the fracture will appear ragged and drawn out. The bearing of this on the strength of the finished paper is considerable. Esparto, straw, and wood, whose ultimate fibres do not exceed 1–2 mm., should, in the majority of cases, appear as whole bast fibres with two tapered ends; the beating, when properly conducted, being confined merely to the separation into these ultimate fibres.