METABOLIC PROCESSES IN THE PLANT. 



273 



the cylinder. The cork has five holes : one for the plant {e.g. 

 maize) ; one for the thermometer, T; one for the dropping funnel, 

 Tr, by means of which 

 boiled-out distilled water 

 can be added as required 

 to the food solution ; 

 one for the in-leading 

 tube, Z, which is con- 

 nected with a worm, 

 and one for the oif- 

 leacling tube, A. To 

 make perfectly air-tight, 

 the space above the 

 cork is filled with a 

 mixture composed of 

 wax, olive oil, and 

 mutton suet, and melt- 

 ing at a comparatively 

 low temperature. Since 

 the culture vessel stands 

 in the large water-box, 

 the regulation of the 

 temperature of the food 

 solution in which the 

 roots are immersed pre- 

 sents no special diffi- 

 culty. The roots must 

 be shaded ; the aerial 

 portions of the plant 

 may remain exposed to 

 the light. Before com- 

 mencing an investiga- 

 tion, we pass a current FIG. lOl.-Apparatus for experiments on the respi- 



of air through the food ration of roots - 



solution for a considerable time (say for four hours), without 

 any preliminary determination of the amount of Carbon dioxide 

 produced by the roots. Since the resistance of the food solution 

 is very considerable, the stream of air must always be a fairly 

 vigorous one (about 8-10 1. per hour). A very large bottle 

 serves for the aspirator. The root system of the large, normally 

 vegetating maize plant represented in Fig. 101 produced at 

 P.P. 



