Although a vast amount of research has been done in the field of carbohydrate chemistry, comparatively little attention has been given to the group of substances which may be classified under the heading of acid polysaccharides. In this group we find such substances as occtins, plant gums, hemioelluloees, mucilages, soluble spoolflc substances produced by bacteria, and alginic acid from algae. Moat of these substances appear to be formed by the modification of cellulose under the influence of enzymes, few, if any of them, being produced directly by photosynthesis. Acid 'polysaccharides apparently play a very important, though poorly understood, role in natural orocesses. In this tlx©ale the structure of the mucilage from rib grass seed, Plantago lanceolate, is investigated. The study falls into two main sections, the first dealing with the products obtained from the free acid mucilage Itself and the second with the products obtained from the ftally methylated mucilage. It Is interesting to note that the British Pharmaceutical Codex (1) asserts that Plantago lanceolate seed gives no mucilage with water. In praotlce, however* aa will be shown later, a 4-5% yield of mucilage can be obtained. How a great deal of confusion arose at one time regarding the exact species of the various Plantago seeds on the market. Plantain seeds are really of Indian origin and in the literature references oan be found pointing to the occurrence of several speoies in native Indien commerce. They are sold in the bazaars under native names and on© of the best known of these is "Bnrtung" or "Barhang". Considerable disagreement has existed as to the origin of this drug, and although Irvine attributed it to Plantago lanceolate (2) research showed that the parent species was Plantago major (3). Another substance which finds extensive use In pharmacy in the East is "Ispaghula", which consists of the dried, ripe seeds of Plantago ovata, a herbaceous annual Indigenous to India end Persia, Psyllium seeds were also regarded as the seeds of Plant a go Psyllium but commercial samples are sometimes composed entirely or partly of seeds of Plantago arenarla or Plimtago lanceolata, Reoent research, published in the quarterly Journal of Pharmacy and Pharmacology gives a quick method of differentiating between the various species of plantain seed (4). It is based on the weights and dimensions of the eeeds and forms quite a good method of oheoklng up on the seeds under observation.