SUMMARYNumerous metachromatic vacuolar granules occur in the hyphae of the fungal symbiont of Taxus baccata mycorrhizas. These granules exist in the trunks and in proliferating arbuscules but they are absent in lysed arbuscules. Direct microanalysis with an electron probe shows that they have a high phosphorus and calcium content. Potassium and magnesium are also present but in lesser quantities. The concentration of phosphorus and calcium is higher in the granules than in the light part of the vacuoles. The concentration of phosphorus also is higher in the granules than in the nuclei of the root, cells and the concentrations of calcium are greater than those measured in the pecto-cellulosic wall of root cells. The role of calcium in the metabolism of phosphorus within the tissues of mycorrhizas still remains unknown.

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Water hyacinth (Eichhorniacrassipes) has demonstrated its ability to remove nutrients and other chemical elements from sewage effluent in the process of producing larger quantities of biomass. This study attempts to compare the incorporation of cadmium in batch experiments or continuous systems. Different concentrations of cadmium (0.25; 0.50; 1.00; 2.00 p.p.m.) were used and toxic effects are obvious at 1.00 p.p.m. concentration. The distribution of the metal was followed in the medium and different parts of the plant. As expected, the roots accumulated the major part (73-86%) of the incorporated cadmium. The change of biomass of different experiments is presented in regard to cadmium concentration.

When the seminal root system of 14-day-old corn (Zea mays cv. Dekalb 202) was subjected to 02 stress, nodal roots with well developed cortical air spaces (aerenchyma) grew into the deoxygenated solution. Microscopic examination showed that there was extensive breakdown of cells in the midcortex of these roots, while the stele, endodermis, and inner layer of cortical cells remained complete, as did the outer layers of the cortex and the epidermis. Occasional files of intact cells, and the wall residues of collapsed cells, crossed the space between inner and outer cortex. Experiments with short, intact root segments with and without air spaces showed that in the presence of 02 the ability to absorb and translocate MRb+, per unit volume or length of root, was llttle affected by cortical degeneration.The distribution across root sections of recently supplied strontium and rubidium, determined by electron microprobe analysis, indicated that in roots with air spaces the strands of wail residues bridging the cortex could be involved in maintaining the conduction of ions from the outer cortex up to the endodermis.In young roots of herbaceous mesophytes grown in well aerated media, gas-filled intercellular spaces normally occupy only a small fraction of the volume of the root. Although tracer studies have established that 02 can move from the aerial tissues and along the gas-filled spaces of the roots (3,14), the amounts of 02 transported are often insufficient for the total requirements of the root system (21, 25), other than in short seedling roots (11). Thus, in roots not specially adapted to 02 deficiency, metabolism continuously depends on supplies of 02 from the rooting medium. Low concentrations of dissolved 02 at the root surface, in equilibrium with 02 partial pressures of only 0.01-0.03 atm are often adequate for root metabolism (2, 10, 1 1), but when the medium becomes anaerobic, root growth and function are inhibited (10,24,28), with adverse effects on shoot development (16,24,28). When deficient aeration is prolonged, adventitious roots, modified by the presence of large air spaces (aerenchyma) formed by collapse of cells in the cortex, grow from the base of the shoot (13,16,19 species including corn, coincides with development of adventitious roots at the base of the shoot (13,16,28). It is thus widely thought that these modified adventitious roots replace the initial root system, damaged by lack of 02, but there have been few studies of whether extensive degeneration of the cortex affects the ability to absorb and translocate nutrient ions and water.In the present research we examined the structure of the modified cortex and determined whether the occurrence of cortical air spaces interferes with the radial transport of ssRb+ across the root to the xylem. MATERIALS AND METHODSPlant Growth Conditions. Corn (Zea mays L. cv. Dekalb 202) was grown in a controlled environment room at a temperature of 18-20 C and a RH of 80-90%. A 16-h photoperiod of 14 klux was supplied by fluorescent lamps. Seeds were ...