CHAPTER X 



THE VARIOUS WAYS IN WHICH PLANTS RESIST THE 

 HOSTILE FORCES AROUND THEM 



Protection 



]Y the methods considered in the preceding chapters, 

 plants provide most effectively for their nutritive 

 needs, and also for advantageous adjustment to the 

 external conditions affecting the same. But they have 

 not thereby solved the whole problem of daily existence, for thej^ 

 still have to reckon with the presence of a great many hostile 

 external conditions. Thus the winds, which in moderation do 

 no damage to plants and even may work them some benefit, 

 occasionally swell to great tempests possessing a power well- 

 nigh too great for resistance. Again, water, which is indispensa- 

 ble to plants in considerable quantity, becomes sometimes, 

 through drought, quite dangerously scant, or through floods 

 quite as dangerously plenty; while various parts and places of 

 the earth, — deserts on the one hand and swamps on the other — 

 though perfectly habitable by plants in all other respects, remain 

 permanently in one or the other of these undesirable conditions. 

 Further, light, which is likewise essential to plants, is in some 

 times and places too weak for efficiency, and in others so intense 

 that unprotected protoplasm can by no means endure it. And 

 again, the food supply manufactured by plants, while ordinarily 

 ample for both themselves and their hereditary dependents the 

 animals, is in some parts indispensable to the continuance of the 

 plants' activity, so that its destruction by animals would consti- 

 tute a serious menace. Finally, while endowed with indefinitely 



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