XI, C, 6 



Copeland: Growth Phenomena of Dioscorea 233 



shoot and so tests the possibility of growing into thoroughly- 

 favorable conditions, following a different line. If this be the 

 explanation, the dying of the tips in darkness may be a more 

 pronounced expression of the same power of the plant to test 

 out a succession of possible lines of growth, instead of consuming 

 its whole food store in an attempt to reach the light with a single 

 attempt. I have observed that branches of Dioscorea luzonica, 

 growing beside my house, reach a limited length and stop rather 

 abruptly under the eaves, but continue to grow much longer and 

 develop as vegetative shoots, if they happen to grow outside the 

 eaves. 



Direct, but not very careful, observation seemed to show that 

 the plants in the laboratory grew as fast during the day as 

 during the night or somewhat faster during the day. Doctor 

 McLean kindly checked this observation by the use of the auxa- 

 nometer with one of the healthy plants of Dioscorea hirsuta, No. 

 331. The results of this test, from 9 o'clock in the morning, 

 May 30, to 9 o'clock in the morning, May 31, with the thermo- 

 graph reading at the same hours, are shown in Table V. 



Table V. — Hourly growth of a healthy plant of Dioscorea hirsuta, No. SSI, 

 during twenty-four hours. 



Time. 



Growth. 



Tempe- 

 rature. 



Time. 



Growth. 



Tempe- 

 rature. 



a. m. 

 9 



mm. 



"C. 

 27 

 27.6 

 28.5 



29.5 



30.1 

 30.8 

 31.0 

 31.1 

 31.1 

 30.6 

 29.8 

 28.6 



p. m. 



mm. 

 6.8 



8.7 

 7.8 

 7.5 



6.5 

 7.3 

 7.0 

 6.0 

 5.8 

 6.6 

 6.3 

 5.9 

 6.4 



•c. 



27.8 

 27.0 

 26.8 

 25.8 



25.5 



25.2 



25.0 



24.9 



24.7 



24.7 



25.9 



26.7 ! 



26.9 



10 



6.8 



8.8 



8.9 



9.1 

 8.4 

 10.1 

 1LS 

 11.6 

 11.5 

 9.5 

 9.2 



10 - 



11 





m. 

 12.... 



J2 .. -- 



a. m. 

 1 .. 



p. m. 

 1 



2 



3 . 



2 





3 





4 





5.. . 





6 





7 





8 









! 



The growth of this plant during the daylight hours was conspic- 

 uously more rapid than during the night, but the distribution of 

 growth is very evidently much more closely correlated with the 

 temperature than with the illumination, which was stronger 

 during the forenoon than in the afternoon. The slowest growth 

 recorded for any hour was from 7 to 8 in the morning, while the 



