548 Brenchley and Jackson . — Root Development of Barley and 
Table IV. 
Wheat . ( Sown February 21.) 
Showing average number of ‘ white ’ roots at different dates. 
Date of 
observation. 
No. of 
weeks 
after 
Unmanured. 
NaNO z . 
Super- 
phosphate. 
Super- 
phosphate 
+ NaNO s . 
Super- 
phosphate 
+ KfSO 4 . 
solving. 
April 13 
7 
1 
2 
2 
1 
3 
April 27 
9 
2 
2 
5 
5 
6 
May 1 1 
1 1 
3 
4 
7 
8 
8 
June 1 
14 
9 
1 
13 
12 
8 
June 15 
16 
18 
1 6 
14 
18 ' 
16 
July 13 
20 
2 
3 
2 
0 
2 
August 24 
26 
0 
0 
0 
0 
0 
The numbers of white roots reached their maximum about 16 weeks 
after sowing. The superphosphate plants were lowest with average 
number 14, while the unmanured and the superphosphate and nitrate 
plants were highest with 18. A certain number of white roots was 
found after this date, but when the plants were mature none was found in 
any of the series. Thus there is in wheat nothing to correspond to the 
sudden disappearance of white roots which occurs in barley about 11 weeks 
after sowing, for in wheat the decline in white root numbers coincides with 
the decrease in weight of the complete root system, whereas in barley the 
formation stops suddenly when the ratio between shoot and root growth 
begins to change. 
Relative growth of Root and Shoot in Wheat . The general behaviour 
of the root and shoot of wheat at different periods of growth proved 
to be similar to that of barley, though the details varied with the different 
manurings (Table V). 
For the first seven weeks growth was very slow and little difference 
in dry weight was observable either between roots and shoots or with 
different manures. During the next four weeks the amount of growth, as 
measured by dry weight, increased considerably, but the shoots did not 
seem to get away properly until after May 11, after 11 weeks’ growth. 
The shoots increased steadily in weight till about a month before harvest, 
when a slackening of the rate of growth occurred except with superphosphate 
and nitrate applied separately. The roots, as in barley, reached their 
maximum long before harvest and then steadily lost weight in every case. 
The striking feature of the pot cultures of wheat was the close similarity in 
dry weight of the unmanured plants and those receiving nitrate only, this 
being obvious both with roots and shoots. Also, the shoots of all plants 
receiving superphosphate, whether with or without other manures, were 
almost identical in weight for 14 weeks, after which those receiving nitrate 
or potash in addition ran ahead of those with superphosphate alone. The 
maximum root growth was attained after about 16 weeks in all the 
manured plants, but the unmanured roots continued to increase in weight 
