THE ATMOSPHERE 77 



absorption resulting from it. Plants which grow in windy 

 situations therefore exhibit xerophytic characters, or they 

 soon perish, and where the wind is incessant and fre- 

 quently violent, tall growth fails altogether, giving place 

 to a low or dwarfed vegetation. This is well seen on 

 wind-swept downs by the sea. On Beachy Head, for 

 example, trees are absent, and the ground is covered with 

 short, thick grass ; what bushes there are are low, stunted, 

 and dense, while the herbaceous weeds scarcely rise above 

 the level of the herbage. It is curious to observe how 

 plants which in the sheltered hoUows and dips grow to 

 their natural size of several feet, sink on the exposed 

 downs to an inch or two, bearing a few leaves,' and 

 perhaps a single flower. But the flower is not reduced 

 in any way ; if anything, its colours are brighter than 

 usual. 



Where trees occur in windy places, they are bent away 

 from the wind, and the branches and foliage develop en- 

 tirely on the sheltered side. This is because the buds on 

 the exposed side do not develop, or, if they do, the young 

 shoots arising from them are killed by the drjring action 

 of the wind. Sometimes a curious phenomenon is wit- 

 nessed. Springing from a broad crown of foliage rises a 

 miniature forest of short, erect, dead twigs. These were 

 shoots which, in their upward growth, just touched a 

 zone where the wind was stronger than their powers 

 of endurance ; they ceased to grow, dried up, and 

 perished. 



Atmospheric Equilibrium. — ^Before leaving the subject 

 of the air, we will refer to a phenomenon which at first 

 sight is not altogether easy of explanation. The world 

 is teeming with life, animal and vegetable. Gases are 

 continually being withdrawn from the air and discharged 

 into it, and yet it is a matter of common knowledge that 

 the constitution of the atmosphere remains practically 

 constant at aU times and in all places. How is this e q^uili- 

 brium brought about and maintained ? We will en- 

 deavour to answer the question by preparing a balance- 

 sheet of the losses and gains of the atmosphere : 



