106 ^^ewcombe, Gravitation sensitiveness not confined to apex of root. 
1) As seen in my own experiments, tlie secondary roots of 
Zea mais on the centrifnge, at a speed of 8 g, assume theii' 
specific angie, not growing in the direction of the radii, wliere 
plasticity wonld carry tfiem. 
2) In nearly every one of tlie experiments recorded in tliis pa- 
per, some roots liave continned to grow straiglit, while otfiers 
have curved outward. Wliy slioiild not all curve, if tlie curves 
are merely plastic? 
3) The roots of Ricinus communis, as recorded ahove, fall to 
bend on the centrifnge even when as little as 1.5 mm are am- 
putated. Yet the roots oiRicinus are most likely as plastic as 
those of Cucurhita or Vicia fciba, which curve after 4 mm 
have been removed. 
4) Unless ^Wiesner’s results can be proved erroneous, he 
has shown the untenableness of the notion of plastic 
curves even at a speed of 41 g, by finding nninjnred roots 
remaining unbent when revolved in a chamber of carbon 
dioxide. 
The only evidence in favor of plastic curving is that offered 
by Brunch or st, when he States that by filling bis revolving cham¬ 
ber with damp sawdust, no curves came on the centrifnge. He 
himself States that the sawdust was wont to become too dry, and 
my own experience proves that not only does the sawdust become 
dry in rapid revolution, but it packs hard against the peripheral 
walls of the revolving dish, and the water passes mostly to 
the periphery, 
But after all this has been said, the reader will still 
feel uncertain of the in direct evidence offered and will look 
for direct evidence. This is given by the following ex¬ 
periments. 
The floor of one of the danip chambers hitherto used was 
covered with thick sheet cork. Nine seedlings of Vicia faha 
had 3 mm excised from their tips and were then fastened 
in the damp chamber in the usual way. On the radially ont- 
ward side of each root, in contact with the terminal 5 to 
8 mm of the root, there was secured by pinning to the cork fioor 
a Strip of cork 15 mm long. This strip of cork wonld Support 
the root, and prevent plastic bending when the centrifnge was 
revolved. 
The revolution employed was at a speed nqual to 8 g for 
each root, the temperature was 24.5 o, and the period 7.5 
hours. At the end of the experiment, 7 of the 9 roots were found 
bent outward atangles ranging from 15 ^ to70o. The other 2 roots 
Avere straight, The 7 roots had curved by lifting their posterior part 
from the cork bar as the tip pressed against the cork, as illn- 
strated in Fig. 5. 
At the time of the examination just recorded, the cork bars 
were removed from the sides of the roots, and the preparation 
was continued in revolution at the rate of one revolution in 3 minutes, 
