THE FOOD OF THE PLANT 7 



given in every case is that taken by the water to move 

 along one inch of the measured glass-tube. 



Ice was then packed round the jar as shown in the 

 photograph. It was at once seen that the contraction 

 of the water due to cooling would upset any readings 

 made for a considerable time. The apparatus was 

 therefore left until the following morning. Most of 

 the ice had then melted and the temperature of the 

 water was kept at 0° C. by the addition of lumps of ice 

 at intervals. It was assumed that by this time the 

 temperature of the water inside the iar was constant. 

 (More accurate readings could perhaps have been 

 obtained by placing the thermometer inside the gas-jar, 

 but this would have necessitated still another fittmg 

 to be kept air-tight.) 



It was necessary to re-wax the apparatus. 



Friday, May 2nd. Dry, windy day. Temp. 0° C. 

 Readings. Intervals. 



P.M. 



1.57 



2.26 29 min. 



2.51 25 „ 



3.20 29 „ 



3.48 28 „ 



Average, 27"75 min. 



The apparatus was then left with the surrounding 

 water so that it might, with as Httle harm to the plant 

 as possible, very gradually regain the normal tempera- 

 ture. 



Further readings were then taken. 



