Turgor and of Temperature on Growth. 399 
temperature between 14 0 and 38° C., whereas a considerable 
decrease occurred by a reduction below 7 0 or 8° C. 
What causes produce these promptly occurring but quickly 
passing changes ? 
A number of possible factors suggest themselves. 
First, the root as a mass of matter contracts or expands 
when exposed to changes of temperature in a manner entirely 
analogous to the changes in length of an iron rod when heated 
or cooled. Determinations of the coefficient of expansion of 
tissues like those here concerned seem to be lacking, but 
judging from those made from wood 1 , this factor is so small 
as to certainly fall within the range of error, and can be entirely 
neglected. 
Second, changes of temperature cause changes of turgor- 
pressure. From experiments made by Pfeffer 2 , it has been 
shown 3 that turgor-pressure is influenced by temperature- 
changes in the same manner as gas-pressure. That is, the 
osmotic pressure increases proportionally to the absolute 
temperature. 
Taking as the coefficient of expansion per degree centi- 
grade 0*00367, or approximately a turgor-pressure of 100 
by a temperature increase of io° C. becomes 103*67 4 . If 
normal roots of Vicia Fab a 20 mm. in length be deprived of 
turgor-pressure 5 by the action for 30 minutes of a 3 per cent. 
KN 0 3 solution, an average contraction of about 2*o mm. 
(drawn from 8 specimens) takes piace. If similar radicles be 
exposed to a sudden change of temperature from 19 0 to i° C. 
the turgor-reduction would theoretically be //g mm. or 0*132 
mm. The average contraction actually found under these 
conditions was 0-035 mm. It is thus plain that the turgor- 
changes due to temperature variations are of sufficient 
L Villari, Annal. d. Physik u. Chemie, Bd. CXXXIII (1868), pp. 412, 417. 
Pfeffer, Pflanzenphysiologie, Bd. II, p. 41. 
2 Pfeffer, Osmotische Untersuchungen, 1877, p. 83. 
3 Van’t Hoff, Zeitschr. f. physik. Chemie, Bd. I (1887), p. 486. 
4 Pfeffer, Zur Kenntniss der Plasmahaut u. Vacuolen, &c. Abh. d. Konigl. 
Sachs. Gesellsch. d. Wissensch., Bd. XVI (1890), Heft II, p. 308. 
5 Pfeffer, Druck u. Arbeitsleistung, p. 297. 
F f 2 
