It is found in the form of its acid potassium salt in many plants, especially in wood-sorrel (Oxalis acetosella) and in varieties of Rumex; as ammonium salt in guano; as calcium salt in rhubarb root, in various lichens and in plant cells; as sodium salt in species of Salicornia and as free acid in varieties of Boletus.
Elongata which produces the " henequen " fibre, or sisal hemp, of Yucatan, silk or tree-cotton (Ceiba casearia), sugar-cane, cotton (Gossypium), indigo and " canaigre " (Rumex hymenosepalus) whose root contains a large percentage of tannin.
These are: Festuca pulchella, Carex microstyla, Salix caesia, Rumex nivalis, Alsine aretioides, Aquilegia alpina, Thlaspi rotundifolium, Saxifraga Seguieri, S.
17); when they proceed at right angles, as in Rumex Acetosella, the leaf is hastate or halbertshaped.
When the development of parenchyma is such that it more than fills up the spaces between the veins, the margins become wavy, crisp or undulated, as in Rumex crispus and Rheum undulatum.