Proteins which combine in vivo with carbohydrates are called glycoproteins. Proteins of this type occur in the glandular secretions of the animal organism and are designated as mucins. Similar protein-carbohydrate symplexes are also found in other organs and are then called mucoids. The general designation “mucoproteins” has been proposed for the protein-carbohydrate symplexes (K. Meyer). Very little is known on the occurrence of glycoproteins in plants. T. B. Osbokne, to whom we owe most of our knowledge on plant proteins, was of the opinion that glycoproteins do not exist in plants. Later it was found that small amounts of glycoproteins can be extracted from the rhizomes of certain plants. These glycoproteins will be discussed with other conjugated proteins (protein symplexes) in volume VIII1.