Biotin is prepared as follows: an aqueous extract of yeast or other micro-organisms, germs and seeds or yolk of egg is either subjected to adsorption by a suitable adsorbent such as fuller's earth, or to precipitation with a water-miscible solvent, in order to remove inactive ballast substances. The remaining solution is subjected to a further precipitation by water-soluble solvents or heavy metal salts, whereupon inactive substances still contained in the solution are removed by acylation, e.g. with acetic anhydride. Then the active ingredients are precipitated with the usual alkaloid-precipitants, e.g. phosphotungstic acid or Reinecke's acid [(NH3)2. Cr.(CNS)4].H. The biotin may be further concentrated by subjecting a solution thereof, preferably an aqueous solution, to adsorption on an adsorbent such as charcoal, and subsequently washing the adsorbate with a watermiscible solvent while adding an alkaline substance. The solution is then precipitated one or more times with alkaloid-precipitants, the precipitates being dissolved in a watermiscible solvent. The product thus obtained may be treated with an alcoholic solution of a mineral acid and the product extracted with chloroform. The chloroform extract may then be extracted with mineral acid and the solution obtained may be subjected to one of the purification methods mentioned above. Crystals of biotin may be obtained by distilling the highly purified product under reduced pressure and collecting the fraction distilling at 185-250 DEG C. under a pressure of 0,001 mm. By saponification of these crystals, methyl alcohol and a free acid is obtained which is a derivative of biotin.ALSO:New media for promoting the growth of plants comprise biotin or its derivatives admixed with, or adsorbed on, inert solid or semi-solid inorganic or organic carriers, or admixed with solid or semi-solid substances stimulating the growth of plants or important for their nutrition, or solid or semi-solid seed dressings. Suitable inert carriers are lime, peat, brown coal, chalk, sodium sulphate, fatty carriers such as wool fat, petroleum jelly, or gum-like substances capable of absorbing water such as agar-agar or tragacanth. Suitable growth-stimulating substances are quinaldine compounds; magnesium chloride, magnesium sulphate, manganese sulphate, potassium chloride; hormones or vitamins, either of animal or vegetable origin or obtained by synthesis, such as hypophysis and thyroid hormones or vitamin B1; or b -indene acetic acid. Suitable plant nutrients are ammonium nitrate, ammonium phosphate and superphosphate. Suitable seed dressing are alkyl, alkoxyalkyl or aryl mercury salts such as the acetates, nitrates, oxalates or silicates, mercury nitrogen compounds, arsenic compounds such as methyl, arsene oxide, quinones, quinhydrones or hydroxyphenyl-hydrazines.ALSO:Manures and seed dressings.-New media for promoting the growth of plants comprise biotin or its derivatives admixed with, or adsorbed on, inert solid or semi-solid inorganic or organic carriers, or admixed with solid or semi-solid substances stimulating the growth of plants or important for their nutrition, or solid or semi-solid seed dressings. Suitable inert carriers are lime, peat, brown coal, chalk, sodium sulphate, fatty carriers such as wool fat, petroleum jelly, or gum-like substances capable of absorbing water such as agar-agar or tragacanth. Suitable growth-stimulating substances are quinaldine compounds; magnesium chloride, magnesium sulphate, manganese sulphate, potassium chloride; hormones or vitamins, either of animal or vegetable origin or obtained by synthesis, such as hyposphysis and thyroid hormones or vitamin B1; or b -indene acetic acid. Suitable plant nutrients are ammonium nitrate, ammonium sulphate, urea, urea phosphate, calcium cyanamide carnallite, potassium nitrate, ammonium phosphate and superphosphate. Suitable seed dressings are alkyl, alkoxy-alkyl or aryl mercury salts such as the acetates, nitrates, oxalates or silicates, mercury nitrogen compounds, arsenic compounds such as methyl arsene oxide, quinones, quinhydrones or hydroxyphenyl-hydrazines. Assisting the germination of seeds.-Seed grain is treated with biotin or its derivatives. The seed grain may be soaked with or caused to swell in solutions of biotin. Aqueous solutions with or without wetting agents, or aqueous-alcoholic or fatty solvent solutions may be employed. The treatment may be carried out in the presence of the nutritive substances, seed dressings, fertilizers or growth stimulating substances referred to above. Biotin is prepared as follows: an aqueous extract of yeast or other micro-organisms, germs and seeds or yolk of egg is either subjected to adsorption by a suitable adsorbent such as fuller's earth, or to precipitation with a water-miscible solvent, in order to remove inactive ballast substances. The remaining solution is subjected to a further precipitation by water-soluble solvents or heavy metal salts, whereupon inactive substances still contained in the solution are removed by acylation, e.g. with acetic anhydride. Then the active ingredients are precipitated with the usual alkaloid-precipitants, e.g. phosphotungstic acid or Reinecke's acid [(NH3)2.Cr.(CNS)4].H. The biotin may be further concentrated by subjecting a solution thereof, preferably an aqueous solution, to adsorption on an adsorbent such as charcoal, and subsequently washing the adsorbate with a water-miscible solvent while adding an alkaline substance. The solution is then precipitated one or more times with alkaloid-precipitants the precipitates being dissolved in a water-miscible solvent. The product thus obtained may be treated with an alcoholic solution of a mineral acid and the product extracted with chloroform. The chloroform extract may then be extracted with mineral acid and the solution obtained may be subjected to one of the purification methods mentioned above. Crystals of biotin may be obtained by distilling the highly purified product under reduced pressure and collecting the fraction distilling at 185-250 DEG C. under a pressure of 0,001 mm. By saponification of these crystals, methyl alcohol and a free acid is obtained which is a derivative of biotin.