144 GROWTH. [CH. VI 



plane of the cotyledons is especially troublesome^ Asken- 

 asy''' uses maize roots for his growth experiments ; he notes 

 that the circumnutation of the roots is in some cases very 

 considerable. 



Read the position of the tip of the root after 10 or 

 15 m. ; and again after a like interval of time ; if the rate 

 of growth is fairly uniform for the two periods, the 

 temperature of the water may be at once raised, if not 

 further readings must be taken. The water may con- 

 veniently be siphoned out and replaced by wanner water. 

 It is best to use water 10° or 12° C. warmer than that in the 

 vessel. The growth of the root will be at once accelerated, 

 becoming nearly three times as quick. It will again fall 

 as the water sinks to the temperature of the room. 



(184) Temperature: roots. 



Repeat exp. 183, substituting water at 3° or 4° C. for 

 the water in which the observations began. Note the 

 sudden and serious check to growth. 



(185) Respiration: roots. 



Proceed as in exp. 183 and when the growth is fairly 

 uniform fill up the vessel so as to cover the cotyledons. 

 Note the rapid fall in the rate of growth, and the recovery 

 when the cotyledons are again exposed to air. 



(186) Temperature: stems. 



The effect of warmth on growth can be well shown 

 with the recording auxanometer. In fitting up the appa- 



^ Power of Movement in Plants, p. 91. 

 2 Deutsche botan. Gesellsch. 1890. 



