220 Influence of Soils, etc., on the Potato Crop. 
Saline mixtures exercise a remarkable influence in promot- 
ing the growth and increasing the quantity of the potato crop in 
some localities. The most striking effects of this kind hitherto 
observed in our island have been produced by mixtures of the 
nitrate of soda with the sulphate of soda, or with the sulphate of 
magnesia. The effect of such mixtures affords a beautiful illus- 
tration of the principle I have frequently before had occasion to 
press upon public attention — that plants require for their healthy 
growth a constant supply of a considerable number of different 
organic and inorganic substances. Thus upon a field of potatoes, 
the whole of which was manured alike with 40 cart loads of 
dung, the addition of 
a. Nitrate of soda alone gave an increase above 
dung alone of - - - - - • 3| tons 
Sulphate of soda alone gave no increase. 
While one-half of each gave ... 5^ tons 
b. Sulphate of ammonia alone gave - - - 1| tons 
Sulphate of soda, no increase. 
But one-half of each gave - - - - 6g tons 
c. Nitrate of soda alone gave an increase of - - 8^ tons 
Sulphate of magnesia alone gave - - • h tons 
And one-half of each gave - - - ' ^i tons 
Such results are very interesting, and if follow^ed up by an ex- 
amination of the quality and composition of the several samples 
of potatoes produced — cannot fail to lead to very important prac- 
tical and theoretical conclusions. 
Failure of seed 'potatoes, — The seeds of all cultivated plants 
are known at times to fail, and the necessity of an occasional 
change of seed is recognised in almost every district. In the 
Lowlands of Scotland potatoes brought from the Highlands are 
generally preferred for seed, and on the bank of the Tyne, Scot- 
tish potatoes bring a higher price for seed than those of native 
growth. This superior quality is supposed by some to arise from 
the less perfect ripening of the ?/^-land potatoes, and by others to 
some peculiar effect or quality of ne-w land, on which skillful 
farmers, who do not import or buy, raise the potatoes they intend 
for the next year's seed. 
These may be in part, true explanations of the fact. The 
better quality of unripe seed may arise from its containing a larger 
per-centage of nitrogenous (protein) compounds, if, as many be- 
lieve, whatever increases the per-centage of starch, increases also the 
risk of failure in potatoes that are to he used for seed. The subject 
is deservino; of further investigation. 
It may be doubted, however, whether the relative proportions 
of starch are to be considered as the cause of the relative values of 
different samples of seed potatoes. This proportion may prove a 
