Priestley and Pearsall . — Growth Studies. II. 243 
that the energy relations of all these reactions are the same, and hence, when 
oxygen supply becomes limiting, all these reactions will not be influenced 
similarly, and the result will be accumulation of C from some such processes 
and the slowing down of others for lack of A and B. 
The immediate consequence will be local accumulations within the cell, 
followed possibly by osmotic action and vacuolation or by the appearance 
of storage products. The general result will be a transition from the active 
growing condition to the resting stage. 
This process of transition to the resting condition occurs most rapidly 
in the region c of the curve, and to judge from a later paper by Slator ( 18 ), 
we may assume that this is in part the result of the accumulation of 
Fig. 3. The increase in weight of roots from cuttings (diagrammatic). Secondary roots 
appear at 2, tertiary roots appear at 3. 
products in some such chemical reactions. These processes are to some 
extent reversible, for if yeast-cells from a culture that has ceased to grow 
are transferred to a fresh supply of nutrient medium, a ‘lag ’ period ensues 
when there is no growth, this being followed by growth at the normal speed. 
This ‘lag’ period is presumably the time required for the removal of the 
accumulation products by diffusion or oxidation. 
Undoubtedly this general interpretation of the existing data of the 
growth of yeast errs on the side of over-simplicity. It gives, however, 
a mental picture of the causal sequences involved, which forms a useful 
background for the attempt to interpret the curves obtained for the growth 
of roots. It has therefore been presented as an introduction to this 
attempt. 
