414 The Woburn Pot- Culture Experiments, 1913. 
As regards the roots, it will be observed from Plate 2 that 
there was a marked difference in the plants to which zinc 
phosphate had been given and those which had received zinc 
nitrate. With zinc phosphate the heaviest dressing produced 
a large root with much feathery development, such as has been 
previously noticed in these experiments where magnesia has 
been used. The smaller applications gave less root development, 
but still more than the untreated. Zinc nitrate, on the other 
hand, produced a quite different kind of root, and one of a 
very stunted nature ; in the case of the application of *03 per 
cent, of zinc the root was found to have gone down onlv four 
inches into the soil. 
From these results it may be concluded that the addition of 
zinc up to 01 per cent, will have, on the whole, a stimulating 
result, and produce better tillering, but that above this amount 
the influence will be one of a toxic nature. 
In the form of nitrate the metal will be more active than in 
that of carbonate or of phosphate. 
(b) The Influence of Copper Salts on Wheat. 
Copper is one of the metals which had not been previously 
experimented with at Woburn. Its extensive use, however in 
agricultural practice, more especially in the form of Bordeaux 
mixture for spraying potatoes, fruit trees, &c., made it desirable 
that an inquiry as to its action on plants should be set on foot. 
This was more especially the case in view of statements which 
have been put forward, as the result of water-culture experi- 
ments, as to the toxic effect of minute quantities of copper 
Co-existing with these was the fact that there is no recorded 
instance of actual damage resulting from the use of Bordeaux 
mixture, although the amount of copper salts transferred in 
this way to the soil in the course of a season must be con- 
siderable. 
The salts selected for trial were the sulphate and the 
carbonate. The pots used were the large earthenware ones 
holding 40 lb. of soil each. The applications given in the 
form of the two salts contained respectively -0025 ner cent 
•005 per cent 01 per cent., -025 per cent., 05 per cent, and 
10 per cent, of copper. Each experiment was in duplicate 
Wheat was sown on November 27, 1912, twelve seeds' per 
pot, and the plants were subsequently reduced to six in each 
pot. 
In the untreated pots the seed germinated by December 16. 
It was only in the case of the heaviest application (TO per cent* 
copper) that the incubation was affected, and here the sulphate 
had a greater effect than the carbonate. In the case of the 
carbonate the first shoots appeared on December 21, but with 
