54 2 Brenchley and Jackson. — Root Development in Barley and 
Shoot/root ratio . The relations between the root and shoot at different 
periods are well brought out by a comparison of the shoot/root ratios. 
Table III. 
Shoot/Root Ratios . Barley . 
Super - 
Super - 
Date . 
Unmanured . 
Sodium 
Super - 
phosphate + 
phosphate + 
nitrate . 
phosphate . 
Sodium 
Potassium 
nitrate . 
sulphate . 
April 20 
i -75 
1.56 
1.69 
1.70 
1-98 
1.58 
1.92 
1.52 
1.32 
i -75 
May 4 
i *45 
i -59 
i *55 
i-68 
1.40 
1.52 
1-45 
1-84 
1.72 
2-11 
May 18 
1-06 
1. 18 
1. 17 
i -43 
i -39 
1.36 
1.28 
1-62 
1-69 
i -37 
June 8 
2-67 
1.87 
2-25 
2-78 
3.02 
2.97 
2-10 
2.30 
2-48 
3-01 
June 29 
3-97 
3-59 
5-47 
3-38 
4-43 
4.99 
3.29 
4.07 
4.70 
4-4 1 
July 27 
10-89 
5-75 
8-07 
6-43 
7.81 
11-48 
6.97 
7-io 
6-o8 
14.49 
August 17 
12-02 
12-05 
12.95 
5.12 
16-23 
For about a month after rapid growth set in both root and shoot 
grew at much the same rate. If anything, root growth was the stronger, 
as the shoot/root ratio had a tendency to fall throughout the period. 
From this time on the shoot grew far more rapidly than the root, and the 
ratio immediately increased, to be followed by a still further rise after the 
weight of the root had reached its maximum and had begun to fall. With 
superphosphate and nitrate, either alone or combined, the disproportion 
between shoot and root was less marked than with no manure or mixed 
minerals (superphosphate and potassium sulphate). (See Table III and 
Fig. 2.) 
The change in the relative ratio of growth of root and shoot is closely 
associated with the change in the morphological structure of the roots. 
The ‘ white 5 roots, described earlier in the paper, were markedly in evidence 
for the first eleven weeks of growth, during which the shoot and root were 
growing at much the same rate, and the shoot/root ratio remained 
practically constant or showed a slight fall. With the increase in the rate 
of shoot growth and the consequent rise in the shoot/root ratio came the 
disappearance of the ‘ white ’ roots — the change being quite sharply marked 
in every case. This change occurred at the same time with all the systems 
of manuring, although the actual amounts of previous growth were so 
different. Possibly this was associated with weather conditions. Prior to 
this time, about May 18, the mean maximum temperature did not rise 
above 6o° F., nor the mean minimum above 45 0 P\ After this the mean 
maximum did not fall below 6o° F., and the mean minimum was usually 
