SECOND KEPOET OS VARIOUS MANURES AT CHISWICK. 155 
tlie comparatively uneven root-growth observed prevents any such 
inference from being drawn. Eepeated experiments under a great 
foot the Professor counted 460 living plants, and the remnants of many others, 
which had succumbed in the encounter. Every year in July the beds were 
examined ; and every year the number of species was found to have diminished. 
Melilots, at first abundant, gradually disappeared ; Arteinisia vulgaris succumbed 
after two or three years ; and so on, till at length only a few species were left ; 
and these not only persisted but had slowly gained ground from year to year, 
and ultimately remained in possession of the plot. The plots under observation 
were 2 metres 30 centim. long, 1 metre broad, all as nearly as possible under the 
same conditions, save that the soil was varied, in some cases consisting of the 
ordinary soil of the garden, in others of an admixture of lime, in others of sand, 
or of sand and lime, and so forth. 
" Of the 107 species under observation all, or nearly all, found the most essen- 
tial requisites of their existence equally well in all the varieties of soil ; so that, 
other conditions being equal, the nature of the soil is indifierent. The species 
which remained victors, all the others being ultimately dispossessed, were : — 
Triticum repens (^Couch), Poa jpratensis, Potentilla reptans, Acer pseudo-platanits 
(Sycamore), Cornus sanguinea, native plants ; and Aster salignus, A. parviflorus, 
Euphorbia virgata, and Primus padus, derived from other portions of the 
garden. 
" It may therefore be inferred that the district in which these experiments 
were made would in process of time, if no obstacle were afforded, become 
covered with meadows and woods — meadows in the low ground, and woods in 
elevated places. Again the experiments show that the survival of certain plants 
has not been influenced by the nature of the soil : thus the Couch-grass was 
ultimately spread over all the plots, whether of sand, or of loam, or of lime, 
whether drained or un drained ; so also with Poa pratensis and Potentilla 
reptans ; so that the chemical and physical nature of the soil, as has been so 
often shown in similar investigations, plays only a secondary part. 
" As to the action of shade, it was found by Professor Hoffmann tliat low-grow- 
ing plants, especially if annuals, disappeared rapidly, while taller-growing plants, 
such as Couch, Primus padus, &c., survived. The survival of certain plants, 
then (Couch, Aster, Potentilla, &c.), is due much less to external conditions 
than to the " habit " of the plant itself — that is to say, to the facility the plant 
has of adapting itself to varying external conditions, and thus of triumphing 
over others less favourably endowed in this wise. 
" The immediate source of victory lies in the powerful root-growth of the sur- 
vivors, including under the general term root, not only the root proper, but the 
offshoots and runners which are given off just below or on the surface of the 
ground. Indeed the latter habit of growth is more advantageous to plants in 
such a struggle than the development of the true root downwards would be- 
Among those plants where the roots were equally developed there were never- 
theless inequalities of growth, dependent probably on the greater need for light 
in some species than in others, &c. 
"It is clear from Professor Hoffmann's experiments that, but for the con- 
tinual use of the hoe, and the diligent extirpation of the weeds in our fields 
