84 ELEMENTS OF APPLIED MICROSCOPY. 



swollen that even the twists cannot easily be seen in a 

 water-mount; they show more clearly, however, in air. 



3. Bast-fibres in General. — Most of the vegetable 

 fibres in commercial use are derived from the bast-layer 

 of the dicotyledonous flowering plants. 



The bast, or, as it is called by botanists, the phloem, is a 

 fibrous layer lying just under the bark, and since it is 

 more or less developed in all the higher plants, it would 

 be theoretically possible to obtain textile fibres from any 

 one of them. In preparing the fibre from those herba- 

 ceous plants actually in commercial use, the stems are 

 first retted or allowed to ferment under water so that the 

 gummy substances which hold the tissues together may 

 be dissolved. Next they- are scutched or exposed to the 

 action of beaters which break up the outer and inner 

 friable tissues, leaving the elongated bast- cells adhering 

 together in threads or bundles. The bast-fibre, as we 

 find it in commerce, is thus made up of a group of cells, 

 not of a single cell like the cotton-fibre. 



When further broken up under the microscope, the 

 bast-cell appears as a more or less elongated spindle 

 with a central canal where the living protoplasm once 

 lay, the cell wall of cellulose only being left. Both ends 

 are symmetrically pointed. In size, proportions, cross- 

 section, canal, and markings the bast-fibres of various 

 plants may be distinguished. We shall consider briefly 

 the six fibres which have most commercial importance — 

 flax, hemp, Manila hemp, jute, ramie, and sisal. 



4. Flax. — Flax is obtained from the stem of Linum 

 usitatissimum, a tall herb widely cultivated in the central 



