Turgor and of Temperature on Growth. 369 
gation only those specimens were used which, by at least an 
average growth, indicated a normal condition. 
As the osmotically active agent, potassium nitrate in 
accurate solutions was used. By means of pieces of cork, 
to which the seedlings were fastened with iron pins or 
rubber bands, the plants were brought in perpendicular 
position into glass vessels containing the desired medium. 
Care was taken that the cotyledons were held above the 
surface and were kept sufficiently moist. Except at times of 
measurement, the vessels containing the seedlings were placed 
in a dark compartment, in which the temperature remained 
fairly constant or made very gradual changes. If not espe- 
cially stated, the range of variation in 24 hours may be 
assumed to be between 1 7 0 and 20° C. 
To obtain the general features of the curve, the growth and 
its distribution were measured in the usual manner by means 
of marks of India ink and a scale. The more detailed study 
of parts of the growth-curve was made with the horizontal 
microscope 1 . Two methods were used: (1) measurements 
were made from point to point, as described by Pfeffer 2 , and 
(2) by the movement of the root-tip on the ocular micrometer. 
A discussion of these methods is given by Pfeffer (as cited), 
Askenasy 3 , and Francis Darwin 4 . 
As the transfer from water to the saltpetre solution fre- 
quently caused a more or less complete obliteration of the ink 
marks, the latter method was here usually applied. 
Some of the sources of error may here receive attention. 
As a sudden change of medium was necessary, experiments 
were conducted only in aqueous solutions with control-experi- 
ments in water. The evident advantages of this method 
seemed to justify its use in face of the fact that the growth- 
1 Pfeffer, Pflanzenphysiologie. Leipzig, Bd. II, p. 84 (1881). 
2 Pfeffer, Physiologische Untersuchungen. Leipzig, 1873, p. 27, also Druck 
und Arbeitsleistung durch wachsende Pflanzen. Abh. d. Konigl. Sachs. Gesellsch. 
d. Wissensch. Bd. XX (1893), Heft 3, p. 293, Leipzig. 
3 E. Askenasy, Ueber einige Beziehungen zwischen Wachsthum und Temperatur. 
Ber. d. deutsch. bot. Gesellsch. VIII (1890), p. 61. 
4 F. Darwin, Arb. d. bot. Instit. in Wurzburg, Bd. II, p. 521. 
