228 MR. F. DARWIN ON THE CONNEOTION 
apical 10 to 12 millim. were curved to a radius of 1 centim., and 
the tip of the root pointed at 459 below the horizon: in No. in. 
the terminal part of the root grew at 75°-80° below the horizon. 
None of the cut roots were geotropic. 
Experiment VILI.—The conditions were the same as in Expe- 
riment VII. 
Split Roots. 
Percentage growth 
Original length. in 223 hours. 
millim. 
lu ees 5 80 
ib cui 5 40 
BE GS oen 55 73 
ba 5 80 
Average ...... 68:3 
Cut Roots. 
L6. 5 130 
do ee 5 140 
Hp ee. e... 5 160 
NS onis 5 160 
Average ...... 1475 
In this case the average percentage growth of the “cut” roots, 
2. e. those whose tips had been removed, is more than twice that of 
the split roots, yet the former showed no clear geotropism, and only 
one of them a very slight curvature downwards. The split roots 
showed a variable amount of geotropism. i. had curved round 
80 as to be bent at right angles in a horizontal plane ; ii. had grown 
horizontally ; iii. showed a distinct tendency to geotropism, though 
its chief eurvature was in a horizontal plane; iv. was strongly 
geotropie, so that the last few millimetres were within a few 
degrees of vertical. After 24 additional hours, i. had become 
clearly geotropic (it is just possible, however, that it was directed 
downwards by growing against its own seed); ii. was only 20” 
below the horizon, but it gave the impression of being clearly more 
geotropic than any of the cut roots ; iii. had its apex pointing at 
609-709 below the horizon. None of the cut roots had become 
geotropic. 
Experiment 1X., 2nd Feb. 1882.— The conditions the same as 
in above cases, except that the marks were made at 2 and 10 
millim. from the tip of the root, so that the measured length was 
about 8 millim. 
