32 THE STRUGGLE FOE EXISTENCE. 



Bajputana ; of Acacia modesta in the Punjab ; of teak in Central 

 India and Bombay ; &c., &c. 



SECTION III. 



THIRD CASE. Mixed crop composed of individuals of one 



and the same age. 



In the two preceding Cases we had to deal with pure crops, the 

 individuals of which necessarily differed from each other only in 

 respect of comparative vigour, size and age. In this, the Third 

 Case, a very complicated element enters, for no two species, how- 

 ever similar to each other they may be, can possess exactly the 

 same habit of growth, or the same requirements as to soil, climatic 

 influences and locality, or the same longevity or vitality, or the 

 same liability to damage from various causes, or equal facility of 

 reproduction, &c. Here we have to consider not merely the strug- 

 gle between individual and individual, but also that between species 

 and species. The conditions which determine the survival of the 

 fittest plants of the crop are hence much more numerous and a study 

 of them is extremely complicated by their acting simultaneously, 

 and often more or less nullifying each other or producing joint 

 effects that sometimes defy analysis. Their consideration is also all 

 the more difficult, as a thorough examination into the working of 

 any one of them is seldom possible without some consideration of 

 some one or more of the rest. In the immediately following pages, 

 therefore, many points will often be anticipated before they are fully 

 discussed in their proper place. Moreover minor details will be 

 omitted as being foreign to the purpose of an elementary Manual. 



The various conditions bearing on the struggle for existence 

 in the present Case will be studied under the following seventeen 

 main heads : 



I. INNATE VIGOUR. Though not absolutely less important here 

 than in the two preceding Cases, this condition has not so far-reach- 

 ing an effect as those which follow, for these latter may, much more 

 so even than a marked difference of individual ages, totally nullify 

 any advantage possessed by a plant in respect of innate vigour alone. 

 This will become rapidly evident with the progress of the present 

 discussion. 



II. GREATER SUITABILITY OF SOIL AND SUBSOIL. The influence 

 of tins condition is extremely great, and is sometimes the sole effec- 

 tive cause of a forest being more or less pure. Thus, for instance, 



