Diaphragms of Water Plants. II. Effect of Certain Factors upon Development of Air Chambers and Diaphragms

Abstract

1. The zone of growth of Scirpus validus is very short, possibly 2-3 mm. 2. The direct contact of the surrounding medium with the growing region is prevented by a closely fitting sheath of scale leaves. 3. In these experiments the rate of growth, in general, was increased by a change from air to water, and from low to high temperature; while the reverse changes resulted in a decrease in the rate. 4. Temperature seemed to be a more important factor than water. 5. The increase in diaphragm distance which followed a change from water to air, and from high to low temperature, did not seem to be sufficiently great to be considered a direct result of the change, inasmuch as there is a normal tendency to increase from tip to base. 6. There appeared to be an inverse relation between diaphragm distance and rate of growth. 7. Environmental conditions may influence diaphragm distance by their effect upon growth. 8. A decreased growth rate would indicate a lowering of the vital activities of the plant, and would result in the formation of fewer diaphragms, thus increasing the distance between them. 9. This decreased vitality was shown normally in the decrease in growth rate toward the close of the growth period, and was accompanied by an increase in diaphragm distance. 10. This plant grew fairly well under 10-20 mm. pressure, while under 60-80 mm. pressure there was almost as good growth as under normal pressure. 11. There appeared to be an increase in diaphragm distance at low pressures. Apparently this was due to the retarding effect of diminished pressure upon growth. 12. Lowered pressure appeared to have no effect upon (1) the total number of air chambers or their size, (2) the thickness of the mass of tissue on the outside of the stem or of the partitions between the chambers, and (3) the number of palisade layers. 13. These experiments lead one to conclude either that water with its low oxygen content is not the direct cause of the air spaces in aquatics, or that Scirpus validus is a very non-plastic organism, retaining its characteristic growth and structure under wide variations in environmental conditions. 14. A lowering of the atmospheric pressure below 630± mm. had a retarding effect upon the growth of Cyperus alternifolius (?), but there is no evidence that it had any effect upon the air spaces.