EXPLANATION OF PLATE XVIII. 



Fig. 1. Fore-period of 6 hours in nitrogen. Geotropic 



stimulation in nitrogen. Afterwards in air during the 



reaction-time. 

 Fig. 2. Seedlings of Sinapis. Fore-period of 4 hours in 



nitrogen. Geotropic stimulation in nitrogen. Afterwards 



in air during the reaction-time. 

 Fig. 3. Fore-period of 6 hours in nitrogen. Geotropic 



stimulation in air. 

 Fig. 4. Fore-period of 8 hours in nitrogen. Phototropic 



stimulation in air. 

 Fig. 5. Fore-period of 3 hours in nitrogen. Geotropic 



stimulation in this gas. 65 minutes after the beginning 



of stimulation nitrogen replaced by air. Then in air 



for a further 55 minutes. 



