54 DOMESTICATED ANIMALS AND PLANTS 



particular instance has no direct effect upon vegetation, but it 

 serves to illustrate the accident of season and its influence upon 

 a new crop of seed. 



Extreme and continued rains at pollination will reduce the 

 yield of corn. 1 A hot wind may have the same effect by kill- 

 ing and drying up the tender young silk before the pollen has 

 opportunity to fertilize. 



Fire plays frightful havoc with vegetation, especially in the 

 forest, and utterly prevents the appearance of certain species 

 on fire-swept lands ; 2 indeed, few can endure a periodic baptism 

 of flame. 



Again, every species has its northern and its southern limits, as 

 well as its limits of higher and lower altitudes. As it nears these 

 limits it not only exists with greater difficulty, but its existence is 

 more precarious, and a little thing will turn the tide for thousands 

 of individuals, perhaps temporarily, perhaps permanently. 



The hard winter not only kills vegetation but freezes up the 

 water supply and often shuts off the food till bird and beast in 

 the melting snows next spring give mute testimony to the 

 sufferings they have endured and the losing fight they have 

 waged, just as a number of years ago the longspurs were 

 caught in passage by a Dakota blizzard and were literally killed 

 by the millions. 



In this general way what may be called the blind forces of 

 nature take their toll of life, and it is a heavy toll indeed, whole- 

 sale and sweeping, relentless as fate and tireless as time. 



Competition for food. After all this, however, a heavy balance 

 remains, — a balance always too heavy for the food supply. 



1 This is due to the fact that the pollen grains stick together and fall in 

 little pellets rather than singly, as they should, in a fine yellow dust, reach- 

 ing each of the thousand silks of a single ear, for every kernel has its in- 

 dependent silk. 



2 The jack pine has taken possession of certain old pine lands only because 

 it has the habit of holding its cones and shedding its seeds gradually. If, there- 

 fore, the tree should be killed, there remains a stock of seed for renewal. All 

 other species are exterminated by these fierce fires till the ground is again 

 reseeded by the slow processes of nature. 



