230 Priestley and Ever shed. — Growth Studies. I. 
were apparent on all roots by July 27. On August 6, after 24 days’ growth, 
the first signs of tertiary roots were visible on most of the plants. 
Series III. These experiments were carried out under the same con- 
ditions as Series II, only that the cuttings belonged to two groups, 45 
cuttings having a mean weight of 5 grm., and 45 of 2*5 grm. No roots were 
removed until after 50 days. The series was started on August 19 and the 
first roots collected on October 8. Only five cuttings were taken each time, 
from each set, so the probable error is larger, but the experiment was 
primarily intended to show the effect of the original mass of the cutting on 
the later part of the growth curve. 
Fig. 2. The growth of roots on Tradescantia cuttings (dry weight). The broken line gives wet 
weight determinations. Arrows show when secondary and tertiary roots appeared. 
On October 8 the roots on the heavier set of cuttings had already 
developed small tertiary roots, but no signs of them were visible in the small 
set until October 15. Reference to the table and curve shows two points: 
1. That the appearance of the tertiary roots in the 2-5 grm. cuttings 
seems to coincide with a flattening of the S curve (see p. 249). 
2. That neither set of roots shows much indication of the development 
of a third S curve. 
The wet weight figures are very irregular, but the dry weight curves 
suggest a third S curve passing at an early date into a flattened region that 
continues throughout the winter. Presumably the root production has 
