164 PLANT RESPONSE 



between 59 and 6o° C. I shall presently have occasion 

 to describe in detail the various characteristics of this 

 curve. 



Having described the apparatus with which these curves 

 were recorded, it is necessaVy to point out the difficulties 

 which were encountered in working with it. It must be 

 remembered that the excursion of the spot of light, in this 

 case, represented a high magnification of the actual move- 

 ments involved. The spot of light, moreover, was re- 

 flected from two separate instruments, and was liable to be 

 disturbed by the slightest jar or tremor in either of them. 

 Though the instruments were placed on a steady stone 

 pedestal, even this precaution could not be made wholly 

 effective, in the heavy traffic of a town. It was only, there- 

 fore, in intervals of quiet that approximately perfect results 

 could be obtained. This difficulty led me to the devising of a 

 much simpler and more perfect instrument, which I shall 

 designate as the Morpgraph} This is a small and portable 

 apparatus, self-contained, in which the necessity of a galvano- 

 meter is obviated. By its means, moreover, the record is 

 unaffected by any earth-vibration. 



The Morograph. — The thermometric record is produced 

 by means of the curling and uncurling of a spiral compound 

 strip, of two metals, having different coefficients of expansion. 

 In order to give strength and steadiness, this helix, which is 

 about 2*5 cm. in diameter, is made of somewhat thick strips 

 of brass and tinned iron, soldered together. By increasing 

 the number of turns in this spiral, the extent of movement 

 per degree in the thermometric record may be increased 

 at will. In my own Morograph, a helix of three circles 

 was found to answer all requirements. The last half-circle 

 of the lower end of the spiral is fixed to a heavy circular 

 stand of brass, 3 cm. in diameter. The topmost half-circle, 

 on the other hand, has had the tinned-iron strip cut off, and 

 therefore consists of brass alone. It will thus be understood 

 that a line drawn diametrically across this last half-circle 



1 This word is derived from the Sanskrit root mrt, Latin mors, death. 



