TRANSACTIONS OF SECTION K. 785 
independence in the programme of this Association, it has, in the aggregate, 
received much attention at the meetings inaugurated with that at York in 1831. 
It is interesting to turn up the early volumes of the Reports, and to ascertain what 
was running in the minds of our predecessors, and what the problems that they 
thought it vital to solve. In the account of the first meeting in this town in 1833 
we find a Report by Lindley on the Philosophy of Botany, two of the items in 
which are of interest to students of Rural Economy. Apparently at that time 
much attention was being given to the mode of the formation of wood. Two 
theories appear to have divided betanists—the one that wood was organised in 
the leaves, and sent down the stem in the form of embryonic but organised fibres, 
to be deposited on the surface of wood already formed. The other theory was 
that wood was secreted zm situ by the bark and older wood. It is to the former 
of these theories that Lindley gives his adherence. Although this problem has 
ceased to interest, the same cannot be said of another subject discussed in the same 
Report, namely, the so-called ‘ fecal excretions’ of plants. In the words of 
Lindley, ‘A new apple orchard cannot be made to succeed on the site of an old 
apple orchard unless some years intervene between the destruction of the one and 
the planting of the other; in gardens no amount of manure will enable one kind 
of fruit-tree to flourish on a spot from which another tree of the same species has 
been recently removed, and all farmers practically evince, by the rotation of their 
crops, their experience of the existence of the law.’ He attributes to Macaire 
the demonstration of the fact that all plants part with a fecal matter by their 
roots. These excretions he held to be poisonous, maintaining that, although plants 
generate poisonous secretions, they cannot absorb them by their roots without 
death, concluding that ‘the necessity of the rotation of crops is more dependent 
upon the soil being poisoned than upon its being exhausted.’ He indicated the 
lines along which investigation might with advantage proceed, one of the questions 
put forward being ‘the degree in which such excretions are poisonous to the plants 
that yield them, or to others.’ 
In 1833 botanists and agriculturists had not the advantage of the knowledge 
that is at our disposal through the continuous growth for a long series of years of 
certain crops at Rothamsted, but consideration of the fact that some crops (as, for 
example, pure forests of beech, silver fir, Scots pine and other trees, as also per- 
manent pasture) may be grown for hundreds of years on the same ground 
without any evidence of poisoning, might have led to the conclusion that the law, 
as it was called, was not of general application. It is, of course, true that rota- 
tions are an advantage, and it is a matter of experience that certain crops—e.g., 
clover and turnips—cannot be grown continuously on the same land, but the cause 
is not now associated with excretions. The reason for the failure of clover, or the 
cause of land becoming ‘ clover-sick,’ as it is called, is still a debated point; but I 
may hazard the conjecture that it is due to the fact that organisms or enzymes 
inimical to the vital activity of the minute living bodies, that exist in symbiotic 
relationship with the clover plants, increase with great rapidity when the living 
bodies that they affect are present in abundance. Red clover is the species that 
is usually associated with the term clover-sickness, but it would appear that a 
precisely similar phenomenon is exhibited in the growth even of wild white 
clover. It isa matter of common observation that on certain classes of land 
white clover is stimulated to such vigorous growth by the use of phosphatic 
manures that for one year at least it monopolises the area to the almost total 
exclusion of other plants. But such rank luxuriance is not of long duration. In 
a year or two the clover disappears to a very large extent, and cannot at once be 
restored by any process with which we are acquainted. The land has, in fact, 
become sick to white clover. But given a period of rest, during which the 
inimical agents will disappear, and it again becomes possible to stimulate white 
clover to vigorous growth. We have, it seems to me, an analogous state of things 
in the case of certain insects. On the Continent the caterpillar of the Nun Moth 
(Iuparis monacha, L.) periodically proves extremely destructive to certain conifers, 
and it is found that in the first year the insects are moderately abundant, in the 
second they are excessively abundant, while in the third the visitation ren to 
1904. E 
