THB MAGAZINE 
OF 
TBG mOOL OF AGRIOULHIRG, 
COLOMBO. 
Adied as a Sapplemeyit monthUi to the '^TEOPICAL AGEICULTUBISTP 
The following pages include the contents of the Magazine of the School of 
Agriculture for July : — 
AGEICULTUEAL THEOEIES AND FACTS. 
E F 0 E E Science and e.specially 
Chemistry lent its aid to explain 
the nutrition and feeding habits 
of plants, there was much specula- 
tion on these subjects, and a 
number of theories were put forward, which in 
the light of our modern scientific knowledge 
appear absurd enough, but judged with regard 
to the position of Agricultural science at the 
time they were propounded, are sufficiently 
stance could not be grown continuously for any 
length of time so as to produce healthy crops, but 
when grown at intervals together with cereals &c. 
they showed no signs of deterioration. This ac- 
cording to De Candolle was owing to the Legumi- 
noscB excreting certain substances which, accumu- 
lating in the soil, became a source of harm — the 
crop then growing in what may be said to be un- 
sanitary conditions ; but the excretions of the 
LeguminoscC were supposed to benefit the Grami- 
nete and vice versa. It is granted that any crop 
grown continuously on the same land without 
plausible. We may notice among others the Ex- 
cretory Theory of De Candolle, which after being 
long abandoned, a coimtryman of the author who 
came to this Island professing ability to cure 
the dreadful coffee-leaf-disease, was bold enough 
to revive. De Candolle founded his theory not 
only on a false analogy but on what we irow 
know are fictions. Having observed that the 
excretions of animals were found useful and bene- 
ficial as supplying the food ingredients of plants, 
and that an animal will not thrive and indeed 
will steadily decline in health if it lived sur- 
rounded by its own excrement, he argued that 
certain families of plants could not continue to 
gi’ow on the sanre land for an unlimited period- 
owing to their excreting certain substances 
which are hurtful to the individuals of these 
families ; but that this excrenientitious matter 
would not be hurtful to other families, and in fact 
would be found bepeftcial. Clover or Beans for in- 
artificial aids, to the exclusion of all others, will 
eventually become less i^roductive and more weak- 
ly and unhealthy ; but Avhat is the reason of 
this ? The theorj’ we are at present concerned 
with, plausible as it appeared in De Candolle’s day, 
did not continue so for long ; for while the Bota- 
nist would not acknowledge that plants were capa- 
ble of excreting substances through their roots 
(as De Candolle supposed), it was further objected 
by those who gave any attention to the matter, or 
made any attempt to test the theory, that no ex- 
cretions of a noxious character could be j^ointed out 
as accumulating in a soil under tlie conditions in- 
dicated. Thus the excretory theory was shown 
to be based on su 2 Jpositions and had no facts to 
support it. It was therefore no wonder that after 
a little time the mere mention of it wa.s received 
with ridicule 
Another theory, which after being accepted with 
credulity inspired by the distinguished author of 
it, was also destined to be abandoned before long, 
was the Mineral Theory of Liebig. Baron Liebig 
held that plants got all their nitrogen from the 
atmosphere which was an unlimited source of this 
most important element of plant-food j the miueral 
