Root Development in Barley and Wheat under 
Different Conditions of Growth. 
* 
BY 
WINIFRED E. BRENCHLEY, D.Sc., 
AND 
VIOLET G. JACKSON, M.Sc. 
(. Rothamsted Experimental Station ). 
With four Figures in the Text. 
I N 1918 our attention was drawn to the occurrence of white roots in wheat 
growing in the field. These white roots were easily distinguished from 
the ordinary type by their thickness, their waxen appearance, and by a lack 
of lateral branches. They were noticed on plants in early spring, and it was 
suggested to us that they form an extra food-supplying system for the 
wheat plants when they are beginning their summer growth. This phe- 
nomenon, however, has been observed at Rothamsted for many years in 
different series of experiments when barley is grown in water cultures. 
The white roots are found fairly abundantly on all the plants when they 
are taken out of their solutions at the conclusion of the experiments, which 
generally occurs before the barley is fully ripe. A typical root system 
under these circumstances shows a number of very long roots of medium 
thickness, which occupy the central part of the system and branch freely 
throughout almost the entire length. On the outer side of the root, 
springing from the tillers, and therefore of later growth, are usually a number 
of ‘ white roots which are much thicker than the others and often reach 
a length of several inches without bearing any laterals. Some of the 
longest white roots bear a few short laterals near the crown. Together 
with these thick roots are thin, delicate ones which begin to give off laterals 
while quite small, and tend to branch well down towards the tip. ‘ White ’ 
roots have also been observed on wheat plants in Broadbalk in early spring, 
occurring earlier in the farm-yard manured plot than on the unmanured. 
The occurrence of these white roots in such widely different circumstances 
as those obtaining in water and in soil cultures led us to investigate their 
[Annals of Botany, Vol. XXXV. No. CXL. October, 1921.] 
