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! 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 ;? indeed, few can endure a periodic baptism 
of flame. 
Again, every species has its northern and its southern limits, as 
well as its jimits 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. 
1This is due to the fact that thé 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. 
? 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. 
