BETWEEN GEOTROPISM AND GROWTH. 227 
periments, in which the growth and geotropie powers of split roots 
are compared with those of * cut" roots, that is, of roots from 
whose apex 1:5 millim. has been cut off. 
The roots were marked at 2 and 7 millim., and the intervening 
9 millim. was measured, at first with the microscope, afterwards 
with an ordinary millimeter-scale. They were all laid hori- 
zontally in a tin box on a surface of damp peat. 
Experiment VII.— 
Split Roots. 
Original Percentage ^ Percentage growth ^ Percentage 
growth in in about 12 growth in 12} 
lengths. about 17 hours. hours more. hours more. 
millim. c . 3 
L ee Du 11 33 25 
HH sn 52 25 38 39 
EE ce 52 35 50 43 
Average ...... 287 403 35°7 
Cut Roots. 
poc 50 60 50 85 
d 50 64 65 41 
MESTRE 53 60 65 32 
Average ...... 61:3 60:0 520 
If we take the averages of the cut roots as proportional in each 
column to 100, we have the following ratios :— 
x E C. 
e 100 100 P^ 
MINUM 387 67:2 n 
Thus we see that the growth of the cut roots is much more 
vigorous than that of the split ones ; nevertheless it is the split 
roots alone which exhibit geotropism. 
After the period of growth represented by column A, no geo- 
tropism was observed in either set. After period B, No. i. 
of the split roots was strongly geotropie, the extreme tip pointing 
Within a few degrees of vertical and the chord of the are made 
by the terminal 6 or 7 millim. being 60? below the horizon ; No. 
ll. was bent sideways and was not geotropic; No. iii. slightly geo- 
tropic, the end of the root being 30° below the horizon. None of 
the * eut" roots were geotropic. After period C the contrast was 
better marked: among the split roots, No. i, which had grown 
less than either of the others, was growing nearly vertically down- 
wards; No. ii. was distinctly, though not strongly, geotropic, the 
