Intracellular air bubbles and interfacial tension inNicotiana miersii

Summary Air bubbles were introduced into living hair cells ofNicotiana miersii. The air entered through wounds inflicted on slightly flaccid trichomes from the base of a fruiting stem. Protoplasmic streaming often continued normally in the threads that were near or apparently touched the air bubble. When air bubbles were included within a plasmolyzing protoplast, the protoplasm nearest the air bubble appeared and behaved like that further away.The volume of an included air bubble is affected by many factors, but as the bubble gets smaller, the overriding factor determining the rate of decrease in volume is the surface tension. The effect of the surface tension on the pressure within the bubble is such that the slope, in a graph of the radius of the bubble to the third power against time, is a constant. The value of this slope constant varies directly with the surface tension, although the surface tension is not the only factor determining its magnitude. The rate of volume decrease of bubbles both in living and in dead cells tended to be constant for small bubbles, and the value of the slope for radius cubed vs. time ranged from – 5 ³/sec. to –14 ³/sec, with most values near –10 ³/sec. A theoretical value for the slope of a nitrogen bubble in water at 25 C. is calculated to be –94 ³/sec. A minimum estimate of the surface tension of the cell content surrounding the air bubble is therefore 1/10th of the value of water.The relatively high value of the surface tension is interpreted to indicate that the organization of the cell content at the surface of the air bubble is not of the structural complexity assumed for the plasmalemma.A portion of this paper was presented at the annual meeting of the Botanical Society of America, Physiology Section, Lafayette, Indiana, 1961.This investigation was partly supported by a grant (G 8716) from the National Science Foundation.