The Physiology of Plants 2: 115 (1903)
Wilhelm Pfeffer

A diminution of the atmospheric pressure usually causes a distinct acceleration of growth in strongly aerobic plants, and this appears to attain its maximal value when the pressure falls to between a quarter and a seventh of an atmosphere. Growth may then be accelerated to two or three times its original rapidity in some plants (Wieler), while Jaccard observed that potatoes grew seven times more rapidly under such circumstances. The result is due partly to the decreased density of the oxygen, and partly to the decreased air-pressure. Experiments performed by diluting air with indifferent gases show that a reduced partial pressure of oxygen does act as an accelerating stimulus to growth, and the fact that different authors are not in precise agreement as to the respective parts played by these two factors probably shows that the duration of the experiments and the nature of the plant are of considerable importance. Wieler found that a mere diminution of air-pressure produced no effect upon growth, possibly because his experiments lasted for a shorter time than those of Jaccard and Schaible. That duration is a factor of great importance is shown by the fact that prolonged tension may at first produce a retardation, but subsequently an acceleration of growth.

It is possible that the decreased air-pressure acts by removing a portion of the external pressure antagonizing turgor, and hence increasing the tension exerted by the internal osmotic pressure upon the cell-wall. In any case, however, the action is a stimulatory one, for a correspondingly increased tension of the cell-wall does not produce any mechanical acceleration of growth. This mechanical theory of Schaible's is in fact based upon an erroneous view as to the importance of turgor in growth. Apparently, therefore, either a decrease of air-pressure or a diminution of the partial pressure of oxygen may act as stimuli accelerating growth, although if the time of exposure is short the period of induction may not be sufficiently prolonged for the production of a perceptible result. [Vochting observed (Bot. Ztg., 1892, p. 94) that a reduction of the percentage of oxygen to 3 per cent, suppressed the formation of root-hairs on the roots of the potato.]

Atmospheric Pressure, Plant Growth & Development