CONDITIONS JTECESSAHT POR A MIXTUBE OF SPECIES. 127 



crop were quite young, these must be entirely killed out wherever 

 the former were numerous enough. 



7. On the quantity and spread of the roots of the several 

 species. — This circumstance always possesses a considerable degree 

 of importance. Some species will always develop a larger mass of 

 roots and rootlets than others. The main roots of some will work 

 their way on horizontally, while those of others will, for the most 

 part, run along through the ground obliquely, and sometimes (as 

 in the well-known instances of sal and jand) even vertically, being 

 thus able to draw nourishment from the deeper layers of the soil. 

 The roots and rootlets of some species are invasive, while those of 

 others, especially while in the seedling stage, wither away in too 

 close contact with the same organs of another species with which 

 they may be growing. These various characteristics and require- 

 ments of the roots of the several species intended for association 

 should be thoroughly considered and allowed for, 



8. In the majority of instances, on the presence of different-aged- 

 individuals. — This point has been explained in sufficient detail 

 under the head of " General Remarks " on pages 83 and 93. 



9. On the characteristic form of the crop and its mode of 

 origin or regeneration. — As regards its form, a crop may consist 

 of only a single story of growth or of two or more stories one above 

 the other ; or it may consist of a single story with an occasional 

 higher tier here and there, or with no individual stems so much 

 more advanced than all their neighbours as to stand in a distinct 

 and isolated manner above them ; and so on. For instance, it is 

 easy to understand that certain species may be able to grow in com- 

 pany with certain others only on the condition that after a certain 

 early age they have their crowns completely exposed overhead and 

 more or less free laterally. Then again, the mode of origin will 

 obviously influence very considerably the permanence or otherwise 

 of a species. Thus, under a strictly simple coppice regime, 

 species producing the strongest shoots or suckers must predominate 

 to the detriment of all the rest ; imder an exclusively high forest 

 regime, the earliest and most profusely seeding species may get 

 the upper hand of every other ; and so on. To sum up what pre- 

 cedes, the form of the crop and the mode of raising or regenerat- 

 ing it should always be so chosen as to suit the mixture in the 

 particidar case in question. 



10. On the relative tenacity of the species to he mixed. — This 

 is too self-evident to require explanation. 



