572 Brenchley. — The Influence of Copper Sulphate and 
The Laboratory distilled water used for ordinary chemical purposes 
exerts a deleterious action on the growth of plants, especially upon the 
roots, probably on account of the fact that it is delivered through copper 
pipes (PI. XLVII, Fig. i). All such water was rejected for experimental pur¬ 
poses, and that used in the preliminary investigations was specially made 
with a glass still. 
Copper Sulphate. CuSo 4 . 5 H 2 0 . 
Experiments were made to ascertain the effect of varying concen¬ 
trations of Copper as Sulphate on the growth of Barley:— 
(ci) in the absence of any nutrient salts ; 
ip) in the presence of a full complement of nutrient salts. 
(a) No nutrients. 
Duplicate series of plants were grown with seven dilutions of copper 
sulphate 1 in distilled water, varying from i : 12,500 to 1 : 1,000,000 C.S., 2 two 
duplicate checks being also made, one in pure glass distilled water, one in 
laboratory distilled water (called for convenience Cu distilled water). In 
these very early experiments, dealing with small numbers of plants, the 
individuals were periodically measured, root and shoot. Later on this was 
abandoned, as the results did not repay the time and labour expended ; the 
method of comparison of dry weights was adopted in its stead and proved 
far more satisfactory. 
In the series under consideration the plants were allowed to grow for 
a month, and it was found that the root and shoot behaved somewhat 
differently with regard to similar concentrations of C.S. Root development 
was entirely checked by every concentration of C.S. from 1 : 12,500 to 
1 : 1,000,000. A little growth had taken place in the Cu distilled water, but 
this did not in any way approach that in glass distilled water. The shoot, on 
the other hand, showed approximately a gradual increase in growth with 
decreasing strength of C.S., the best growth occurring in the glass distilled 
water. These results seem to indicate that the barley root is very sensitive 
to minute traces of copper sulphate, even one part in 1,000,000 being 
sufficient to check growth. It is evident, though, that even the strongest 
concentration, 1 : 12,500, does not actually kill the plant, at any rate at once, 
since the shoot continues its growth to a certain extent, living on the reserve 
materials in the grain. Similar results were obtained from a second set of 
plants grown later on in the year. 
(b) With nutrients. 
Duplicate series of plants were grown with similar concentrations of C.S. 
as under (a), but containing a definite quantity of nutrient salts in addition. 
1 For convenience CuSo 4 .5H 2 0 is expressed throughout as C.S. 
2 All concentrations are expressed in grams of CuSo 4 .5H 2 0 to cubic centimetres water. Thus 
1 : 12,500 C.S. means 1 gram CuSo 4> 5H 2 0 crystals to 12,500 c.c. H 2 0 . 
