590 
Rotation of Crops. 
have modified his view considerably ; and to have supposed 
that the explanation was- — not that the excreted matters of one 
description of plant were injurious to another of the same 
description, but that, as the different plants had such very 
different mineral requirements, the alternation of one kind with 
another relieved the soil from exhaustion. In his latest work, 
however, after many years of controversy, he obviously more 
fully recognised that nitrogen probably played some important 
part in the matter. 
More than fifty years ago Boussingault published the 
results of an investigation, extending over a period of ten 
years, to determine the chemical statistics of some of the 
rotations actually followed in his own locality, in Alsace ; 
and he came to the conclusion that the difference in the 
amounts of nitrogen taken up by the different crops constituted 
a very important element in the explanation of the benefits of 
rotation. 
We can only further briefly refer to the results and conclu- 
sions of the late Professor Daubeny, of Oxford, who commenced a 
series of experiments in the Botanic Garden there in 1834. One 
of the original objects he had in view was to test the truth of De 
Candolle’s theory that the excretions of one description of plant 
were injurious to plants of the same description. He soon came 
to a negative conclusion on the subject ; and recognised the 
validity of Boussingault’s argument that the actual facts of 
vegetation in different parts of the world conclusively showed 
that the same description of plant may continue to grow 
healthily on the same land for long periods of time. On this 
point it is scarcely necessary to add that the experience at 
Rothamsted on the growth of various agricultural crops year 
after year on the same land for many years in succession is 
conclusive against the theory of injurious or poisonous 
excretions. 
But, as already said, Dr. Daubeny continued his experi- 
ments for ten years; and although, in accordance with the 
prevailing ideas of the time, all his analytical results related to 
the mineral constituents of his soils and crops, his main con- 
clusion was, that the benefits of rotation were^ probably as much 
connected with the available supply of the organic as of the in- 
organic constituents. 
What, then, are the indications of the results of many years 
of investigation of the subject, in the field and in the laboratory, 
at Rothamsted ? 
