Distribution of Calcium Oxalate Crystals in Ricinus Communis in Relation to Tissue Differentiation and Presence of Other Ergastic Substances

Abstract

1. The development of calcium oxalate crystals and their distribution in the mature green plant, in etiolated shoots, in green and in etiolated seedlings, is examined in relation to tissue differentiation. Two types of crystals are present, druses and solitary crystals. The former are distributed throughout parenchyma tissues in general; the latter are practically restricted to the secondary phloem, where they are deposited chiefly in vertical files of cells adjacent to the phloem fibers. 2. The development of a druse may be traced from a single crystal at the limit of visibility within a protoplasmic strand, through an aggregate or dendritic type of growth to a miniature druse, and finally to a mature crystal entirely filling the cell. Sheaths of undetermined composition may be detected around very small crystals about 3 μ in diameter. The sheaths of older druses consist of cellulose and are occasionally partly suberized. They are attached by stalks to the cell wall. Solitary crystals are also surrounded by cellulose sheaths. 3. Crystal idioblasts grow more slowly than adjacent parenchyma cells, and intercellular spaces appear around them in the youngest internodes. In contrast to this, fat idioblasts expand rapidly, maintain contact with surrounding cells, and intercellular spaces do not arise until later. 4. Crystals develop in the growing shoot about the level of the third node, and they rapidly increase in number in the differentiating primary stem. They reach their maximum concentration in the vascular networks of the nodes and leaf blade centers and along the leaf veins. Crystals are also distributed more or less regularly throughout the pith and are present also in the cortex and vascular parenchyma of the stem and of the petiole. They occur occasionally in the lamina and are frequent in the caducous stipular sheath. This greatest density of crystal deposition coincides with the maximum distribution of fat idioblasts and of sugar. 5. When secondary thickening is established in the stem, druses become masked by starch grain deposition in the pith and occasionally elsewhere. In many cases the crystals are dissolved and leave behind them the empty crystal sheath. At the same time starch accumulates and may completely fill the former crystal idioblast. 6. In contrast to druse behavior within the older stem, solitary crystals appear abundantly in vertical files of parenchyma cells adjacent to the phloem fibers in the secondary phloem. 7. In the root, except in the cortex near the origin of secondary roots, druses are practically absent. Solitary crystals, however, occur in the secondary phloem. 8. Druses are present in the pith of the young inflorescence axis approximately as in the stem. Since nodal vascular networks are absent, however, the crystals do not equal those of the shoot in number. As the seeds develop, starch deposition in the fruiting axis is extremely heavy; here, as in the older stem, druses may dissolve and disappear. 9. In the fruit wall, calcium oxalate crystals are not abundant at any stage of development. In the seed, one or two small crystals may appear near the caruncle but do not occur elsewhere. 10. In the etiolated shoot, crystal distribution is similar to that in the green, but the number of crystals is markedly less. 11. In green seedlings, crystal development is slight, a few at the cotyledonary and first plumular nodes, rarely in the parenchyma of the hypocotyl, and occasionally in the cortex of the root. 12. In etiolated seedlings, crystals are practically absent. A few very small druses may be detected at the cotyledonary node. They are absent throughout the hypocotyl, and the plumular node does not develop. 13. Crystal distribution is discussed in relation to various factors, such as: calcium supply; tissue metabolism as indicated by the presence of fat, sugar, and starch; cell-wall thickening; hydrogen-ion concentration.