298 ScHREINER AND REED: EXCRETIONS BY ROOTS 
WHEAT SUCCEEDING OATS. 
The results of the preceding experiments point quite distinctly 
to the conclusion that the waste products of some plants are only 
slightly toxic to wheat seedlings. It seemed desirable to test 
oats, a more closely related species to wheat than either of the 
other two tested, and one which in agricultural rotation is a bad 
crop to precede wheat. 
Oat seedlings were allowed to grow for 8 to 10 days in non- 
nutrient agar, which was then melted for use as in preceding 
experiments. 
(a) Wheat plants in tubes containing fresh agar and surrounded 
by agar in which oats had grown.—The accompanying table 
shows the results of four experiments comprising 87 roots. 
| 
Experiment No. | Roots Capable of Roots Which Grew 
periment No | Responding. Oat of Tobes. Per Cent. Response 
Be ee ee aie < 
| Riemer 
‘ | 21 = Sa 
? | 34 I 9 ; 56 
; = 6 40 
4 | 17 8 \ 
47 
Average for the four samples of agar, 49 per cent, 
It will be noticed that only 49 per cent. of the roots grew out 
of the tubes into the agar in which oats had grown as against 66 
per cent. in the case of the fresh agar in the experiments already 
given. 
(2) Wheat plants in tubes containing agar in which oats had grown 
and surrounded by fresh agar. The following table gives the re- 
sults of four experiments which are complements of those given 
under “a.” 
Se 
Eapertaret ie: Roots Capable of | Roots Which Grew | tent. Response: 
| Responding. Out of ‘Tubes, | Per Cent. Resp 
| Dia ion ac 
: | 24 | 16 | 67 
: | 21 | 13 62 
3 t 45 \ 2 3 | 5 I 
4 19 Sane. | 33 
Average response for the four samples of agar, 61 pet cent. 
The results of these experiments show that the agar in which 
oats had grown was more toxic than that in which corn oF cow- 
peas had grown. When oats agar was used the proportion of 
