56 BOTANICAL GAZETTE [JANUARY 
in the table. It will be noticed that carbon black shows the same 
tendency to produce abnormal root growth as does ferric hydrate, but 
to a less marked degree. 
Experiment III included very finely pulverized quartz flour, as 
well as ferric hydrate and carbon black. The two last named bodies 
showed here the same abnormal acceleration of root growth as was 
previously observed, but quartz flour, although it improved the 
general growth of the plants, produced no such effect. 
iG. 1.—Experiment II; 24 wheat plants grown 19 days. 1, Extract of Leonard- 
town foals 2, the same with calcium carbonate; 3, the same with ferric hydrate; 
4, the same with carbon black; 5, the same with magnesium carbonate; 6, the same 
with barium carbonate. 
The experiment with ferric hydrate and carbon black has been 
repeated many times with extract of Leonardtown loam, as well as 
that of other soils, and always with the same result. In some cases 
acceleration of root growth is more marked with carbon black than 
with ferric hydrate, but usually the reverse is true. 
Experiment IV was carried out with an aqueous extract, prepared 
as above, from Miami silt loam collected at the Rhode Island Experi- 
ment Staticn, at Kingston, R. I. This soil had been in hoed crops 
