64 TIJAXSACTION.S OF THE [Sess. lxxx 



2. Opuntia occkh'ii falls. 

 12th May to 4th June 1914. 



Tlie natural conditions were, at this time, sixteen hours' 

 light to eight hours' darkness. Opuntia occidentalis tran- 

 spires considerabl}^ during the darkness period — the ratio 

 of transpiration in light to that in dark being as 1:*37, 

 while the ratio of light to dark is as 1 : -5. The hourly- 

 graphs show on an average a maximum of transpiration 

 at 8 p.m., a minimum at 4 p.m., wdtli subminimum at 1 a.m. 



8. L Ilium riihrwm. 



1st May to 21st May 1915. 



The plant at this period would be subjected to sixteen 

 hours' light and eight hours' darkness. The hourly graphs 

 show that the maximal values of transpiration occur at 

 7 o'clock in the morning and 2 o'clock in the afternoon, 

 the minimal values at 9 p.m. and 9 a.m. The ratio of 

 transpiration in the light to transpiration in the dark is 

 on an average as 1 : "22. 



B. The Ejfccf of DdrlriK'ss on Transpiration. 



The types Pimuh .sylvestri.s and Lilium rubruni were 

 experimented upon in the dark room, and in both cases 

 the transpiration was found to l)e very erratic. In spite 

 of the absence of light, transpiration was very active, and 

 there was evidence of a periodicity, although it was very 

 variable. 



SUMMAIIY. 



1. Under normal conditions there is a daily periodicity 

 in transpiration. 



2. 'I'his periodicity varies in the three types experi- 

 mented upon. 



3. Under all dark conditions tr-anspiration is active but 

 erratic. 



I liave to thank Mr. H. A. Robertson for his kind 

 assistance in the ai'ran<,nni; of tiiese results. 



