182 
On Rape-dtist 
plant, — an operation of greater value to stiff soils than to free 
ones.* 
5th. That we should not apply large quantities of rape-dust at 
a time, because the active decomposition may, in such case, 
destroy the germ of the seed, or cause the produce to yield a 
coarse and light-weighing sample. The effect of young plants 
being too largely supplied with rich organic manure is well known. 
The plant is stimulated to an increased action at one time, which 
the other matters in the soil cannot maintain ; and the consequence 
is that the seed is deficient in some of its constituent elements, 
and the straw soft and unproductive. 
The case instanced by Professor Liebig, of a vineyard having 
been thus stimulated by the action of organic matter, is an illus- 
tration of the principle, f 
* Moreover, strong soils are naturally the best wheat soils, and will 
make the most sure return for any extra application on the wheat crop. 
Again, we have shown that plants require a liberal supply of azote or 
nitrogen to perfect the seed ; now wheat requires more than either barley 
or oats ; all of them, however, require it at the latter stages of their 
growth, so that the fact that decomposition goes on more slowly in clay, 
and that consequently the nitrogen of the manure will not escape so 
quickly, is another reason why rape-dust seems most efficacious for wheat 
on stifi' soils. 
Dr. Madden, in his excellent essay ' On the Application of the Prin- 
ciples of Vegetable Physiology and Chemistry to Agriculture,' uses this 
argument as one of the ]}rohabiliiies why wheat seems to require a clay 
soiL If, however, the retention of azote be, in this case, one probable 
explanation, it appears to be a positive one why rape-dust should answer 
best for wheat on such soils, when it is considered that, owing to its ten- 
dency to decomposition, the azote which it contains is so liable to be 
quickly evolved. 
t A case in point occurred last year, on the farm of a relative of mine. 
On a very hungry limestone soil, he drilled barley with from 8 to 12 bushels 
of rape-dust per acre. The field had grown turnips the ])receding year, 
and the crop had been consumed by sheep on the land during the winter. 
On the brows of the hills, where the niagnesian marl is not more than two 
inches from the surface, he spread mi extra quantity of rape- dust from 
the hand. Throughout the spring, and the summer, the crop looked 
well generally, but the brows of tlie hills presented a most luxuriant ap- 
pearance, being several shades darker in colour, and much longer, than 
the other parts of the field. In the autumn, however, it was discovered 
that the promising prospects were not to be realized. The supply of 
organic matter had been so great that it had forced the growth at a quicker 
rate than the soil was able to supply the other requisite inorganic mat- 
ters ; the consequence was, that the straw was so soft that it was not able 
to bear its own weight. Long before harvest it lodged on the ground ; 
