4g THE STBTTGGLE FOE EXISTENCE. 



some species develop a close matted mass of roots and rootlets, which 

 strangle the roots of associated species growing with them. Others 

 again also possess abundant spreading underground stems, which 

 render them all the more invasive. Thus the roots and rhizomes 

 of species of Carets, Andropogon, and many other grasses form a 

 felt-like mass, often several feet thick, which strangles out all other 

 growth. Once bamboo has taken possession of the soil, few indivi- 

 duals of other species can force their own roots through the dense 

 tangled mass of its fibrils and root-hairs ; and, conversely, when 

 both the soil and locality are suited to the growth ef bamboos, no 

 individuals of other species which keep their roots within the same 

 depth oi soil can co-exist with them, only such trees as can spread 

 out their roots below the layer monopolised by the bamboos having 

 a chance of maintaining a permanent footing in the crop. Hence 

 the frequent inability of teak, Terminalla tomentosa, and other spe- 

 cies possessing more or less horizontally spreading roots to cope 

 with bamboos, which cannot, however, keep out sal and other trees 

 with deeper-seated roots. 



This last example introduces us to, and also illustrates, another 

 point, viz., the relative depth to which the roots of the various asso- 

 ciated species can penetrate a circumstance that has a most import- 

 ant bearing on the distribution of some of our most valuable species. 

 To cite further instances, teak, the Terminalias, &c., as we know, 

 spread out their roots within only six feet and often less of the sur- 

 face, so that in shallow soils resting directly on a dry subsoil, they 

 yield the place to Boswellia, Anogeissus, khair, Prosopis spieigera, 

 &c. The Prosopis spicigera has been known to force its main roots 

 down to 60 feet and more below the surface of the soil, and is, ac- 

 cordingly, able to flourish in the dry plains of the Punjab, whither 

 hardly any of its companions of moister regions can follow it. Again 

 the sal is one of the few trees that can grow on the waterless bould- 

 er deposit at the foot of the Himalayas, the tap root of that species 

 being able to penetrate down to a depth of 60 feet and even more; 

 and this fact accounts for its generally forming much purer forests 

 there than inside the hills. Many of the trees of the dry tracts of 

 India, which bring out their leaves in the height of the hot weather, 

 like the Bassia latt/oh'a, Buchanania lit/folia, &c., have been known 

 ID -end down their dense network of fibrous rootlets to 20 feet below 

 the sin-fa^, in onler to attain the stratum of permanent moisture. 



( 'onlming ourselves to the consideration of young seedlings alone, 

 it M ay lie hud down as a general rule that the longer the taproob 

 developed by the yearlings of a given species is, the better will they 



