Recently McRARY and TRAUB (16) isolated a fructosan, or levulosan, tentatively identified as inulin, from guayule plants. Later HASSID et al. (11) definitely characterized this fructosan as inulin. Further work on the water soluble reserve carbohydrates of guayule has shown that in addition to inulin, levulins are also present, and in relatively greater amounts. The application of the principles developed in the present paper to physiological research problems by the authors and others (39,40,3,5,6,7) has shown that the fractionation of the levulins into 89% ethanol soluble and insoluble portions may be used as a more dynamic tool in plant physiological research than the mere recording of total residues. The preliminary results concerning the free monosaccharides in guayule and the analytical methods for determining the water soluble carbohydrates in guayule are slummarized elsewhere (41, 39).According to McRARY and SLATTERY (15), continuous extraction, for six hours, of the finely ground guayule tissue when 80% ethanol by volume is placed in the boiling flask of the extraction apparatus (Landsiedl type), completely removes the "reducing sugars and sucrose" leaving the "fructosan" in the insoluble residue. Under the conditions indicated, it should be pointed out that the condensate dripping into the extraction cups is approximately 89% ethanol by volume (9) and is approximately at the boiling point of the solvent. In order to show that the interpretation of McRARY and SLATTERY (15) is untenable, previous work on the naturally occurring polysaccharides in some Compositae will be briefly reviewed, the water soluble carbohydrate reserves in guayule will be considered, and the fractions separated from guayule by McRARY and SLATERY (15) will be critically examined.
Previous workIn 1870, Popp (24) reported a "soluble modification of inulin" in the tubers of Heltiacrthu,s tubTerosus which he named "inuloid." Since that date apparently the nature of the inulides (inuloid) or levulins in plants and their relation to inulin, and also the characteristics of inulin as it occurs in nature, were little understood until the subject was elucidated in 1932-1933 by SCHiUBACa and KNOOP (30).Although TANRET (35,36) in 1893 reported that he was able to separate from inulin associated matter (pseudo-inulin, mol. wt. 2610; inulenin, mol.