296 ScHREINER AND REED: EXCRETIONS BY ROOTS 
When the seedlings had attained a length of 5 cm. they were 
planted thickly in dishes of soft agar. At the expiration of 10 to 
15 days the seedling plants were removed and the agar melted for 
experiments in the manner previously described. 
(a) Wheat plants in tubes containing fresh agar and surrounded 
by agar in which corn had grown,— The accompanying table sum- 
marizes the results of four experiments, As much as 59 percent. 
of the wheat roots capable of response curved out and grew out 
of the tubes away from their own excreta into the agar containing 
the excreta of the previous corn crop. 
Pirneriment No. Roots Capable of Roots Which Grew : : 
cg cabana oa | Responding. Out of Tubes. | Pee Cont: ee 
i 13 7 54 
2 20 10 50 
3 13 9 69 
4 23 iy 61 
A ee 
Average response for the four samples of agar, 59 pet cent. 
(6) Wheat plants in tubes containing agar in which corn had 
been grown and surrounded by fresh agar. — Four experiments 
were likewise performed in this series. Here 62 per cent. of the 
roots curved and grew out of the tubes. The details are shown 
in tabular form. 
Experiment No. Roots Capable of Roots Which Grew Response. 
Responding, Out of Tubes. | Per Cent. ae 
: 24 16 67 
: K fod 18 56 
: 2 6 
Average response of the four samples of agar, 62 per cent. 
These results obtained from the use of agar in which pop-com™ 
had previously grown showed that such agar is decidedly less 
toxic to wheat than the agar in which wheat had grown. In all 
cases where pop-corn agar was used a high per cent. of roots 
curved and grew out of the tubes. The figures obtained, 59 and 
62 per cent., stand notably near that obtained when only freshly 
prepared agar was employed, namely 66 per cent. The percent- 
ages obtained in series “ a’ and “4” are the proportion of 9 5:100, 
the difference lying within the limit of experimental error. This 
