In recent numbers of the Penny Journal, Martin Doyle has published two valuable papers upon the necessity of selecting good seed, and I would wish to call the attention of the cultivators of flax, who form so numerous a body amongst the small farmers of the north and west of Ireland, to the absolute necessity of attending to the seed of that plant, and not to purchase the cheaper seed that is sometimes offered to them, in preference to that which, although rather more expensive, is yet free from the seeds of a very noxious weed which are usually mixed with the cheaper flax-seed. The weed to which I refer is one of those curious plants, which, from their peculiar structure, are unable to draw their nourishment directly from the earth, but are obliged to feed themselves by sucking the juices of other plants, and thus destroying them, or weakening them so greatly as to prevent their producing a crop that will repay the cultivator for his labour and expense. In the case of the flax, the weed grows from seeds deposited in the earth with the seed of the flax, and at first appears as a slender pale thread, twisting about in different directions until it meets with one of the stems of the flax, when it immediately twists itself round it, and produces curious little knobs upon its inner side, which pierce the outer coat or bark of the stalk of the flax, and suck from it the juices which it has drawn from the ground, and prepared for its own nourishment. The root of the weed then withers away, but the weed itself commences its most rigorous growth, for until it had obtained a victim upon which to feed, it had been unable to produce any thing except the slender fibre that I have already mentioned, and would have soon died if it had not succeeded in seizing upon the flax. Its stem then increases in thickness, and, twisting round all the flax plants that it can reach, it receives enough of nourishment to produce its flowers, which form pretty little yellowish white heads, of about half the size of a nut, consisting of numerous small flowers so placed together as closely to resemble a small mulberry in form and appearance, although not in colour. This weed is called Dodder, or by botanists _Cuscuta epilinum_, and is commonly to be found in flax-fields in several parts of England and Scotland, but is happily less frequent in Ireland, although I have seen it (in 1840) in the county of Mayo. In England it often quite destroys the crop, and I understand that such was the case a few years since in the neighbourhood of Westport and Newport, county Mayo.