Flax.This class, although embracing a variety of substances, was not an extensive oae, the chief and most interesting features relative to vegetable substances having been those comprised in the growth and manufacture of flax and hemp, including preparations by Claussen's patent. Of the flax plant there are several varieties in cultivation, the best seed coming from the Riga and Holland. As the different varieties arrive at maturity at different times, and the stem rises to different heights, it is very essential that the seed be not mixed, as this would occasion great inconveniences and loss in the pulling of the flax. The most common variety of flax in Great Britain is ot a moderate length, with a strong stem. If it is not sown very thick, it will throw out branches at the top, and produce much seed. It is, therefore, a matter of calculation whether it will be most profitable to have finer flax, with less seed, or an inferior quality of flax and an abundance of seed. There is a small variety which does not rise above a foot, grows fast, and ripens its seed sooner. When the principal object is to get linseed, this variety is preferred ; but the flax is shorter, and also coarser. The soil best adapted to the growth of fiax is a deep, rich loam, in which there is much vegetable mould. It should be yellow, and loose to a considerable depth, with a sound bottom, neither too dry nor too moist. Either of these extremes invariably destroys the flax. It is, therefore, not suited either to hot gravelly soils, or cold wet clays ; but any other soil may be so tilled and prepared as to produce good flax. The land should also be free from weeds, as the weeding of this crop forms a very important item in the expense of cultivation. These circumstances suggest the following mode of preparing the land : A long fallow, including two winters and a summer, will be a good preparation for the heavier loams, which should be trenched plowed, and worked deep. The manure generally used is rotten dung, or a .compost of earth and dung, or some artificial dressings. If the land is sufficiently clean, a crop of potatoes, well manured, may be substituted with advantage for the fallow. Flax has also been found perfectly successful, when grown after clover, on a single plowing, especially if the clover be biennial. The stubble, of the clover is plowed up, either in the spring or autumn, with some care, and then the harrow and roller are passed over the ground before sowing., If the soil contains a great portion of clay, lime may be used with advantage ; but in the lighter loams it may be dispensed with. At all events, it should not be used immediately before the flax is sown, but for some previous crop. Peat ashes make an excellent manure, as they Improve the soil and keep off insects, which are apt to injure the root of the flax. For the want of peat ashes, those made by the burning of weeds and earth in a smothered fire are a good substitute. There is another manure, also, which has been found to answer exceedingly well, composed of the sweepings of streets in towns, mixed with night soil. Where night soil cannot be obtained in sufficient quantities, rape cakes, from which the oil has been expressed, dissolved in cows' urine, form a very excellent manure. When the flax begins to get yellow at the bottom of the stem, it is time to pull it, if viry fitte flax is desired, such as is made into thread for lace or fine cambric; but then the seed will be of little or no value. Every flax-grower judges for himself what is most profitable on the whole. The pulling is done carefully by small handfuls at a time. These are laid upon the ground to dry, two and two, obliquely across each other. Fine weather is essential to this part of the operation. Soon after this they are collected in larger bundles, and placed with the root end on the ground, the bundles being slightly tied near the seed end. The other end is spread out, that the air may have access, and the rain not damage the flax. When sufficiently dry they are tied more firmly in the middle, and stacked on the ground till the next season. Some carry the flax, as soon as it is dry, under a shed, and take off the capsules with the seed by rippling. Sometimes, if the capsules are brittle, the seed is beaten out by means of a flat, wooden bat. The flax is then, according to the usual process, immediately steeped. By Claussen's invention, this method, to a certain extent, is dispensed with, the pure fibre being more easily and rapidly separatd from the wood. As this process has excited great at-iention, both in this country and Europe, it is certainly deserving of a fair trial. In order explain it as far as possible, we cannot, perhaps, do better than to use the Chevalier's own words. [Here follows a very long article from the 1 Morning Chronicle ;" a pamphlet published by Mr. J. Wylie, of this city, contains a far better description of the process. It appears ;o us that our Commissioner's information on such an interesting subject as flax should not be second hand. The Claussen flax cotton, ifter all, it turns out now, cannot be spun on cotton machinery. Specimens of Woad.This plant was once cultivated to a great extent for the blue dye extracted from it, but has been greatly superseded by indigo. It might still be cnl-Sivated to great advantage, as it improves the color ot indigo when mixed with it in a certain proportion. The plants, when just about flowering, are mown with a scythe, washed with water and sun dried ; after this they are ground into a paste, which, kept in heaps for about a fortnight, is then formed and pressed into solid balls. It is also occasionally sown as food for cattle, and has lately been recommended for this purpose under the name of pastel. Its vigorous growth and hardy nature are in its favor ; but it will only flou-rish in very rich soils. [The Woad Plant, we believe, is cultivated in some parts ot the United States.