106 PLANT LIFE ON THE FARM. 
in a mixed manure a particular effect is due, and to ob- 
tain confirmation of the results obtained by other 
methods. By adding or by withholding a particular salt, 
as the case may be, an answer to the question proposed 
may be obtained. In the following paragraphs the effects 
of the disuse of certain manures, and then of the substi- 
tution of one kind for another, will be very briefly allud- 
ed. to. 
Disuse of Manure of any Kind.—On a plot to which 
farm-yard manure was applied it was observed that while 
the produce was largely increased, more so indeed than 
under almost any other circumstances, the per-centage 
‘of grasses and of some of the miscellaneous weeds was 
increased, while the leguminous herbage was diminished. 
‘On discontinuing the dung the vegetation of the plot 
was observed gradually but uniformily to approximate 
-to that of the unmanured plot, the number of species 
increasing without any marked preponderance of any, 
and good grasses like Poa trivialis giving place to poorer 
ones, such as Festuca ovina. 
Disuse of Farm-yard Manure.—Another plot which 
originally received a combination of dung and ammonia, 
has been treateg since 1864 with a small dose of ammonia 
salts only. Here the grasses and the Leguminose are 
diminishing as to numbers, but the luxuriance of those 
species that remain is increased. The miscellaneous 
weeds, especially Rumex Acetosa, and the Composites, 
are decreasing, Rawunculacew decline, and even more 
markedly so the Umbellifere and Plantago lanceolata, 
the latter plant being very sensitive to ammonia. 
Disuse of Potash.—The first effect noticeable after 
the disuse of potash was a diminished produce of grasses. 
Leguminose have also continuously and strikingly de- 
