12 BOTANY 



Indirectly the composition of the above-ground part 

 of the plant has a direct application to a danger to which 

 the underground region is exposed. The pressure of 

 the wind upon an unyielding surface in the air would be 

 attended by great danger to the anchoring root, which 

 might be violently pulled from the ground by the 

 leverage exerted by such pressure. The great subdivi- 

 sion of the shoot system and the flexibility of its ultimate 

 twigs minimises this danger, but even as it is, it is not 

 unusual after a tempest to find even sturdy trees up- 

 rooted and thrown down. 



The distribution of the water of rain-storms presents 

 another problem which must be solved by the shoot 

 system. The water can be led either towards or away 

 from the centre of the plant. Should the root system 

 be one which spreads considerably and extends to long 

 distances below the surface of the soil, it is of great 

 importance that the rainfall collected on the central 

 mass of shoots shall be distributed widely so as to reach 

 as far as the extremities of the roots, watering in this 

 way a large area of ground. If the root system consists 

 of a strong main root with comparatively few branches, 

 this arrangement would largely deprive it of water. 

 Hence in plants with roots distributed in this way we 

 find arrangements to conduct the water into the centre 

 of the mass of shoots. 



In some rare cases the duty generally discharged by 

 the root as an anchoring organ falls upon the shoot, 

 which then is partly developed underground. Such a 

 stem bearing in its turn appendages has a special name 

 it is called a rhizome. 



If we pass to a closer study of the much divided or 

 branched shoot we find almost invariably that its ulti- 

 mate twigs put forth certain regularly arranged flattened 

 expansions. In cases where there is much exposure to 

 currents of air, these flattened portions are furnished 



