THLASPI, MITHEIDATE, or Treacle mustard; a genus of the siliculosus order, belonging to the tetradynamia class of plants. There are 10 species; of which the most remarkable are, 1. The arvense, or penny-cress, is a native of several places of England and Scotland, growing in corn-fields, but not very common. The stalk is a foot high, angular and branched; the leaves sessile, embracing the stalk at their base; the flowers very small and white. The plant smells of garlic; and in countries where it abounds, is found often to communicate its disagreeable odour to the milk of cows that feed on it. The seeds abound with an oil formerly used for the rheumatism and sciatica, but now taken no notice of. 2. The bursa pastoris, or shepherd's purse, is common in corn-fields, gardens, waste places, and by way-sides. This plant affords us a strong instance of the influence of soil and situation; for in some places it is not more than two inches high when it flowers and perfects its seeds, in others it rises to the height of two or three feet. It is insipid; but was nevertheless formerly much recommended in haemorrhagies of all kinds, though deservedly rejected in the present practice.