As the fruit approaches maturity, these fibres lose their cylindrical form, becoming ribbon-shaped through the collapse of their walls, and at the same time each fibre twists on its axis, thus causing a sufficient pressure on the interior of the boll to burst it at the junction of the compartments in the outer casing. [Illustration: FIG. 2.] [Illustration: FIG. 5.] [Illustration: FIG. 1.] [Illustration: FIG. 3.] [Illustration: FIG. 4.] [Illustration: FIG. 6.] After being left on the trees for some days, during which time the ripening influences are at work, increasing the convolutions and maturing the fibre--or exposed perhaps in the case of unfavourable weather to the damaging influence of rain, which stains the cotton, or intense heat which renders it brittle, or wind which fills the boll with sand or leaf--the cotton is picked. It is then passed through a gin, a machine which has for its object the separation of the fibre from the seed. This latter, which in medium-stapled cotton exists in the proportion of 2lb. seed to 1lb. fibre, is used up at the oil-mills--while the cotton is packed in bales of 4cwt. and forwarded to the sea-coast for export. The foregoing may be taken as a condensed description of the cultivation of cotton on an American plantation. In Brazil and Egypt the season is about a fortnight later; in India planting generally commences in July, or immediately after the dry season. The raw fibre then is a ribbon-shaped filament with corded edges twisted with 300 to 800 convolutions to the inch; thus, although to the naked eye appearing quite smooth, under the microscope it has somewhat of a resemblance to the shape of a joiner’s auger. Fig. 1 represents a typical cotton fibre about 400 times the actual size, and Fig. 2 represents its section. Fig. 3 represents an immature or imperfect fibre, one which is more transparent, brittle, and weak than the ordinary fibre, with no tendency to take dye. The convolutions also are few and irregular. Fig. 4 represents its section. The longest fibre is the Sea Island cotton grown off the coast of the States, averaging 1-5/8 inches in length, and chiefly spun into 150’s to 400’s yarn, although for experimental purposes 2150’s have been produced from it. Egypt gives three varieties--brown, white, and Gallini. The first-named is commonest and is used for 50’s to 150’s wefts and twists. The American States yield a comparatively clean and even-running cotton, the best variety being Orleans, of a mean length of 1-1/16 inches, used for 30/40’s T and 30/60’s wefts. Texas, though shorter, is from its strength used for warp yarn, while the numerous varieties classed as uplands or boweds are suitable for weft on account of their usual good colour and cleanliness. The difference between the white 60’s and 70’s wefts and brown ditto is that the latter is from brown Egyptian cotton. Brazilian is a very harsh fibre about average length, and used for twists either alone or mixed with American.