xi, c. 5 Copeland: Growth Phenomena of Dioscorea 229 



However, while the behavior of the different plants from the 

 time that a sprout became active until its growth ceased, or 

 at least slackened, had so much in common that in a general 

 way it can be described as uniform in its larger features, there 

 was such irregularity in the time at which this occurred that 

 the difference, which would appear at any time between average 

 growth in darkness and average growth in light, would have 

 been an expression of the number of plants that happened just 

 then to be active, rather than of a difference in growth under 

 the influence of the illumination. Some plants started, reached 

 their maximum rate, and nearly or quite ceased to grow; while 

 others remained quite inactive, but retained their power of 

 growth, as proved by subsequent behavior. 



Tables II and III shown the growth in millimeters, for one 

 day, May 8-9 and for one week, May 9-16, respectively, for 

 each of the plants. The exceeding irregularity is seen at the 

 first glance. While these tables contain many blanks/indicating 

 that the plants in question had not begun to grow, there were 

 very few of the entire lot of roots that did not grow before the 

 experiment was discontinued, about the end of June. 



There was no rule as to which plants would grow first, except, 

 perhaps, that a large tuber was likely to germinate earlier 

 than a small one ; even to this rule, there were so many exceptions 

 that it would not be worth while to pair the tubers by size and 

 to expect them to be comparable in rate of growth at any partic- 

 ular time. Some varieties on the average germinated sooner 

 in darkness and others in light. On the whole, germination of 

 the plants in soil was quicker in darkness than in light. This 

 was possibly due to the soil having been kept wetter in the 

 dark room ; but there was no intention to do this. In the light 

 the plants of more than half of the varieties germinated more 

 slowly in the bamboo tubes than on the open table. In spite of 

 this, my conclusion from observation of the whole series is that 

 germination can be hastened somewhat by moisture, but is in- 

 dependent of illumination. 



In spite of the diversity of figures in Tables II and III and 

 of the further fact that this diversity would be the same if any 

 other days or weeks were chosen for presentation, I believe that 

 one may conclude from all of the figures that the rate of growth 

 of young shoots of Dioscorea is independent of the light. Pfeff er, 

 probably on Sachs's authority, says that this is the case. The 

 average growth of all cultures, as has already been noted, was 



