POPULAR SCIENCE REYIEW. 
that certain plants, flowers, and fruits, attain far greater perfec- 
tion in our gardens than they ever do in their native countries. 
That a war of extermination is thus going on around us may 
strike some with surprise. They are so accustomed to asso- 
ciate flowers and plants with peace and repose, that they are 
astonished to find that other far less amiable ideas may, witli 
even more justice, be associated with them. And yet a 
moment’s reflection, or a passing glance at the nearest hedge- 
row or pasture, will show the reality of the struggle. All that 
beautiful disorder, that apparently careless admixture of divers 
forms and colours — the sweeping curves of the brambles, the 
entwining coils of the honeysuckle, the creeping interlacement 
of the ground ivy or the pennywort — all are but indications of 
the fray that is constantly going on. It would seem as if the 
weakest must succumb, must be overpowered by the stronger- 
growing plants, and so they are at certain places and at certain 
times ; but, under other conditions, the victory may be with 
the apparently weaker side, just as the slow-going tortoise may 
outrun the fleeter hare. In any case the success is often only 
temporary ; the victor becomes in time the vanquished ; the 
vanquished, in its turn, regains its former conquest ; and so on. 
It is proposed in the following notes to give a few illustra- 
tions of the nature and effects of this conflict, of the way in 
which it is carried on, and of the circumstances which 
favour it. 
Agriculturists had long been practically conversant with the 
advantages derivable from the practice of not growing the 
same crop on the same soil for too long a period. The advan- 
tages consequent on this so-called rotation of crops are due to 
more than one cause ; but it was Bureau de la Malle who, in 
1825, called attention to the phenomenon of natural rotation. 
From long observation of what takes place in woods and 
pasture-lands, he established the fact that an alternation of 
growth, as he called it, occurs as a natural phenomenon. In 
pasture-lands, for instance, the grasses get tlie upper hand at 
one time, the leguminous plants at another ; so that, in the 
course of thirty years, the author whose observations we are 
citing was witness of five or six such alternations. 
It follows from all this that a plant, as was pointed out by 
the late Dean Herbert, does not necessarily grow in the situa- 
tion best adapted for it, but where it can best hold its own 
against its hostile neighbours, and best sustain itself against 
unfavourable conditions generally. 
The sources of success in the contest are manifold; they 
vary more or less in each individual case. Probably they are 
never exactly the same ; nevertheless, there are certain circum- 
stances which must always be operative in conducing to the 
