ess MR. F. DARWIN ON THE CONNECTION 
necessary for the “ induction ” of a heliotropic curvature are the 
same as those necessary for the completion of the curvature. 
In the following abstract of some of Wiesner's results the 
figures given are the average increase in length per cent. in 
24 hours of four normal and four “ cut ” roots (i. e. those whose 
tips have been cut oft). 
Maize. 
Normal, Cut. 
"Nus 41, or as 100 to 53:9. 
Peas. 
42:7 9:7, or as 100 to 227. 
Vicia Faba. 
90 60, or as 100 to 667. 
In repeating Wiesner's experiments, I have thought it best to 
take shorter periods of growth, since geotropic curvatures are 
generally completed long before 24 hours have elapsed. 
Experiment 1., Jan. 17, 1882.—Six roots of Vicia Faba, from 
2-3 centim. in length, were marked at 8 millim. and again at 
11 millim. from the tip; 1:5 millim. was then cut off three of 
them, and the length of about 3 millim. between the two marks 
was measured with a weak objective and eyepiece-micrometer. 
The eyepiece was divided into large spaces each equivalent to. 
'875 millim. ; and by estimating the 4jlths, the rate of growth 
could be expressed in units equivalent to ‘0375 millim. When 
the roots became too much curved to be thus measured, the growth 
was taken with a pair of compasses and a millimeter-scale. During 
the experiment the roots were placed horizontally on damp peat 
,in a small tin box. 
Cut Roots *. 
Percentage Percentage 
Original growth in growth in 
lengths. lh.50 m. 2h.20 m.additional. 
millim. 
m 25 6 17 
a 26 4 11 
Bh noo 2:0 4 14 
Average... 47 14 
* The roots whose tips had been amputated are called “cut” roots. “ Per- 
centage growth" during a given period is obtained by reducing to 100 the 
length of the measured portion at the beginning of that period. 
