xi, c, 5 Copeland: Growth Phenomena of Dioscorea 237 



marks, growth should cease each day at the back end of the 

 growing region, in zones having a total length about equal to the 

 day's total growth. I noticed years ago, that published figures 

 by as careful a worker as Sachs do not stand this test, but that, 

 if one might judge from the figures, the total elongating region 

 is much longer on the second day than it was on the first. Since 

 noticing this, I have always made it my practice to check meas- 

 urements occasionally by remeasurement after a second day. 

 This kind of check is illustrated by the measurements on plant 

 "Light Soil No. 1," Dioscorea hirsuta No. 331, May 23-25, shown 

 in Table VII. 



Table VII. — Growth of the same zones on successive days. 



[Dioscorea hirsuta. Light Soil No. 1, May 23-25.] 



- - 



Centimeter zone. 



Growth, 

 first day. 



Growth, 

 two days. 



Centimeter zone. 



Growth, 

 first day. 



Growth, 

 two days. 



1 



mm. 

 5 

 8 

 12 

 12 

 14 

 IB 

 19 

 19 

 15 

 14 

 12 

 9 

 8 



mm. 



14.. 



mm. 

 6 

 5 

 4 

 3 



2.5 

 2 

 2 



1.5 

 1 



0.5 

 0.5 

 0.5 



mm. 

 6 

 6 



2 . 





15 . . 



3. . 





16 



4 





17.. 





5 . 





18 



13.5 

 2 



6 





19 . 



7... .. 



34 

 26 

 17 

 15 

 13 

 9 



8 



20 . 



8 



21 . 





9 



22 . 





10 



23 - 





11 . 



24 





12 



13... 



25 











' 



Analyzing these figures, it appears that the growing region the 

 first day was 25 centimeters long. At the end of the second day, 

 zone 11 extended 25.4 centimeters from the apex, and was the 

 last zone that showed any increase in length. In other words, 

 the figures checked in this case and the length of the growing 

 region was unchanged. 



Many of the plants in darkness had a short apical portion 

 rather sharply bent. This was usually not more than 1.5 centi- 

 meters in length. Repeated observation showed that the move- 

 ment of these apical segments was quite irregular, which agrees 

 with Newcombe's observations. The most remarkable behavior 

 shown was that of occasional plants that kept the bent part at 

 nearly the same angle and in the same direction, while the stem 

 as a whole was growing. The movement of this apical part 

 resulted sometimes in a twisting of the stem and at the other 

 times did not do so. Dioscorea aMa is a remarkably convenient 

 subject for the observation of twisting. 



