294 SCHREINER AND REED: EXCRETIONS BY ROOTS 
used agar was tested against freshly prepared agar, the segmented 
glass tubes being filled with one and surrounded by the other. 
The mode of procedure was as follows: Clean segmented tubes 
were placed in a jar of liquid agar and when it had cooled to the 
proper temperature a seedling was placed in the mouth of each 
tube. When the agar had hardened throughout the entire jar, the 
tubes could be removed without disturbing the seedling or losing 
any agar from the tubes. The tubes were transferred to vials con- 
taining the other sort of agar which had cooled to a temperature 
between 30° and 35° C. When this agar was completely hardened, 
the vials were wrapped in black paper and put upon the klinostat. 
The quantity of agar in which plants had grown was always sepa- 
rated into two portions, one of which was used within a set of 
tubes and the other portion without another set of tubes. This 
procedure made each set of results a control on the accompanying 
results. Thus, the experiments designated under each heading as 
“a” constitute a check against those designated as “b” and vice 
versa. 
WHEAT SUCCEEDING WHEAT. 
(a) Wheat plants in tubes containing fresh agar and surrounded 
by agar in which wheat had been grown. The used agar was ob- 
tained and prepared in the manner outlined above. Five experi- 
ments were conducted comprising 89 roots. The details are given 
in the accompanying table. 
—— 
Experiment No. | eo ee. of | une Rieke Per Cent. Response. 
I 8 fe} 10] 
2 22 | 12 55 
3 12 | 2 16 
4 | 32 13 40 
5 15 4 26 
ose Ee ae 
Average for the five samples of agar, 27 per cent. 
It will be noted that an average of only 27 per cent. of the 
roots which grew as far as to the first opening in the tube, turned 
and grew out into the surrounding agar, in which wheat plants 
had previously grown, as against 66 per cent. when fresh agat we 
also used on the outside, as in the experiment already described. 
(2) Wheat plants in tubes containing agar in which wheat had 
