Wheat under Different Conditions of Growth. 553 
system of rooting in wheat is vertical and that wheat roots may normally 
run down to a depth of 4 ft., whereas barley and oats tend to show a com- 
paratively light and shallow growth. This is common experience, but the 
factors which cause the difference need examination. 
In the pot cultures both wheat and barley behaved in the same way 
with regard to the depth of penetration. The first-formed roots, branching 
freely, soon reached the bottom of the pots, and, continuing their growth 
with much less branching, coiled round the bottom and gradually formed 
an interlaced mat of roots in the larger plants. The pots were 14 in. deep, 
and for about that distance strong concentration of laterals occurred, no 
difference being observable between the two species. The consistent results 
obtained showed that the limiting factor to strong lateral production in this 
case was the depth of the pots ; also the total length of the roots when 
uncoiled was much the same in both plants. It must be borne in mind that 
in these pot-culture experiments the soil was carefully sifted and shaken 
into position, but not rammed. Watering was carefully and regularly done, 
so that water-logging did not occur, and thus the plants were growing in 
a friable, well-aerated, moist soil, and did not suffer either from drought or 
excess of moisture. Under these favourable conditions heavy root growth 
was made, and barley proved able to develop as deep and strong a root 
system as wheat within the limits imposed by the pot. In both cases the 
unmanured plants had weaker roots than the manured, except that sodium 
nitrate failed to improve the root growth of wheat. 
The field experiments, with barley, revealed quite a different state of 
affairs. The Rothamsted soil is heavy, and on the plots examined the tilth 
was poor, so that below the first inch or two the soil became very con- 
solidated and about five inches down passed into clayey undisturbed subsoil. 
Under these conditions little tillering of the barley shoots occurred, and the 
roots when washed out were very thin and poverty stricken. The number 
of roots springing from each seed was small, they were thin and but slightly 
branched, and did not penetrate very far into the soil in a vertical direction. 
Instead they tended to go off at an angle, to run more or less horizontally 
with a downward inclination, and to take advantage of any easier passage, 
such as that offered by a piece of straw in the soil, a worm track, or the 
cavity struck out by the underground part of a strong growing weed such 
as Convolvulus arvensis or Cirsium arvense. The whole root system when 
washed out was very small and offered no comparison with that of the pot 
plants. The results were the same for unmanured and superphosphate plots 
at the time the barley was ripe and from similarly manured plots on which 
the barley was still green. Practical experience suggests that the roots 
would have been somewhat larger at an earlier stage, but the shoots showed 
conclusively how poor the root must have been even at its best. 
It might be objected that when the roots were washed out in situ 
