EXPLANATION OF PLATE XIX. 



Fig. 1. Fore-period of 3 hours in nitrogen, in which 



phototropic stimulation. 75 minutes after the beginning 



of stimulation nitrogen replaced by air. Then in air for 



a further 65 minutes. 

 Fig. 2. Fore-period of 8 hours in 4.3 % oxygen, in 



which geotropic stimulation. Then in air during the 



reaction-time. 

 Fig, 3. Fore-period of 24 hours in 4.3 % oxygen, in 



which geotropic stimulation. Then in air during the 



reaction-time. 

 Fig. 4. Fore-period of 10 hours in 4.7 7o oxygen, in 



which phototropic stimulation. Then in air during the 



reaction-time. 

 Fig. 5. Fore-period of 24 hours in 4.7 '^/q oxygen, in 



which phototropic stimulation. Then in air during the 



reaction-time. 



