\yo 



PLANT RESPONSE 



till one degree of rise of temperature produces a horizontal 

 movement equal to i inch. After this, keeping the distance 

 of the recording surface constant, the length of the short arm 

 of the Lever, to which the plant is attached, is so adjusted 

 that the vertical magnification is two hundred times. The 

 length of specimen used, unless the contrary is stated, is 

 always 5 cm. A movement of the 

 light-spot through a vertical distance 

 of one division ('i inch) will then 

 represent an expansion or contraction 

 of one part in two hundred of a 

 specimen whose length is 5 cm., that 

 is to say, one part in a thousand of 

 a specimen whose length is one 

 centimetre. In fig. 85, the original 

 record has been reduced to one- 

 fourth. The distance between two 

 horizontal lines represents a contrac- 

 tion or relaxation of 1 per cent. 



In order to exhibit the differences 

 in the characteristic curves of different 

 specimens, or of the same specimen 

 at different ages, I append three re- 

 cords taken under the same standard 



Fig. 87. Thermo-mechanical conditions : (D) that of the Style of 

 Records or s, Young Speci- v ' * ~ 



menotspirogyra ; s' Older Datura alba ; (s) of a young specimen 



Specimen of same; and r cr. • 1 /„r\ r ij 



b. Style of Datura alba of Sptrogyra \ and (s') of an older 



The distance between two specimen of the same (fig. 87). In 



horizontal lines represents these three experiments, the rate of 



a contraction or relaxation F 



of 1 per cent. rise of temperature and other circum- 



stances having been the same, it is 

 instructive to compare the different parts of the different 

 curves. 



Taking first the curve of Datura, we find its death-point to 

 occur at 6o° C. The relaxation undergone by the specimen 

 during the rise of temperature from 35 C. to the death- point, 

 was at the mean rate of 2*1 parts per thousand per degree for the 



