7 6 THE POPULAR SCIENCE MONTHLY. 



of an Alexander; and the results of the wars of the plants are as- 

 suredly of no less importance, seeing that the very existence of an 

 Alexander depends in no slight degree upon them. The campaigns 

 we speak of are real; they are not mental figments, or allegorical 

 illustrations. Success in the practice of horticulture, of agriculture, of 

 forestry, depends on the action we men take toward the combatants. 

 If we remain neutral, the weakest goes to the wall, overpowered by 

 the stronger ; if we interfere, we exert a very powerful influence for 

 the time ; but, immediately we cease to exert our power, the combat 

 begins again, and with enhanced violence. The essence of successful 

 cultivation often consists almost entirely in the removal of the plant 

 from the influence of that hostile " environment " to which, under 

 natural circumstances, it would be subjected. It is this that accounts, 

 in a great measure, though of course not wholly, for the oft-observed 

 fact 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 associate flowers and 

 plants with peace and repose, that they are astonished to find that 

 other far less amiable ideas may, with 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 colors 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 suc- 

 cumb, must be overpowered by the stronger-growing plants, and so 

 they are at certain places and at certain times ; but, under other con- 

 ditions, 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 van- 

 quished; the vanquished, in its turn, regains its former conquest; and 

 so on. 



It is proposed in the following notes to give a few illustrations of 

 the nature and effects of this conflict, of the way in which it is carried 

 on, and of the circumstances which favor it. 



Agriculturists had long been practically conversant with the ad- 

 vantages derivable from the practice of not growing the same crop on 

 the same soil for too long a period. The advantages consequent on 

 this so-called rotation of crops are due to more than one cause ; but it 

 was Dureau de la Malle who, in 1825, called attention to the phenome- 

 non of natural rotation. From long observation of what takes place 

 in woods and pasture-lauds, 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 the upper hand at one time, the 



