No abstract

Measurements of the growth rate of intact lupin seedlings were made under steady-state conditions and as the environment was altered. Although the growth rate frequently changed smoothly with the new condition, there were several cases where periodicity or oscillations in the growth rate were observed. These cases included growth oscillations induced by: the solution in which the roots were immersed being changed back from a mannitol solution to water; the replacement of anaerobic conditions by air or oxygen; the tension being increased on the hypocotyl; and, under some condi- tions, the addition or removal of high CO2 concentrations. The observed periodicity is more complex than is accounted for by a simple relationship of the minimum yield stress increasing or decreasing with the growth rate, but more information is needed to develop a better model.

A theory of the freezing process of the tissue of pear fruit is presented, based on the cell permeability theory and on the thermodynamics of moisture in porous media. According to this theory the nature of the temperature v. time curve during freezing is determined by the speed of advance of the ice front into the tissue. Curves for freezing and thawing calculated from the theory are compared wit,h experimental curves.