Turgor and of Temperature on Growth. 401 
exposure is necessary to induce a depression. The duration 
of this depression increases roughly with the increased period 
of exposure. 
The character of this occurrence seems to suggest a cause 
that one would regard as probably present. It seems plain 
that in the depression-period we have the reaction of the 
living organisms to a stimulus, here represented by the ex- 
posure to the low temperature and the shock of the sudden 
change. 
It is not to be forgotten that a prolonged stay in a low 
temperature may induce in the plants a sort of pathological 
condition, and that we are then no longer dealing with normal 
objects h 
When changes were made between 18 0 and 30° C. as 
extremes, evidence of retardation following was not to be 
detected. The modified rate of elongation following a change 
of temperature would be fully accounted for by the changes 
of turgor-pressure having their origin in the differences of 
temperature. The irritable response to change, if present, is 
lost in the accidental irregularities of growth. In this case, 
we must agree with Pedersen 2 , that temperature-change as 
such has no perceivable effect on plant-growth. 
R ecapitida tion. 
The most important results of the second part of this paper 
are here briefly summed up. 
Following a sudden fall or a sudden rise of the temperature 
between i8*o°-su *o° and o*5°-i-5° C. as extremes, the first effect 
seen is a slight turgor-change due to physical causes, pro- 
ducing, or tending to produce, a shortening in length if the 
temperature be lowered ; or, in case the temperature be raised, 
producing an elongation. 
Following this mechanical action, a period of depressed 
growth usually follows. The duration of the depression-period 
depends on the position of the lower temperature-limit and 
1 Pfeffer, Druck und Arbeitsleistung, p. 354. 
2 Pedersen, loc. cit. 
