PLATE LXXX 
Fig. i—Stomatoscope designed by Dr. F. E. Lloyd and used for a part of these 
studies. 
Fig. 2.—Humidity box in place over plants in the greenhouse for maintaining dif¬ 
ferent relative humidities. Also a cog psychrometer used for checking hygrothermo- 
graphs kept among the sugar-beet plants. 
