56 THE PRINCIPLES OF AGRICULTURE". 



period without germinating, until the hull is accidentally 

 scratched, or broken, so as to admit moisture. This may 

 account for the fact that so many weeds unexpectedly 

 and repeatedly spring up after the soil is stirred in cul- 

 tivating crops. 



2. Warmth. There is a certain range of temperature 

 within which a seed will grow, and outside of which it 

 will fail to do so. 



The seeds of some plants, whose native home is in cold 

 climates, will sprout at a low temperature, while others, 

 which are accustomed to a warmer climate, require a 

 higher temperature. The lowest point of temperature at 

 which wheat, barley, oats, and peas will sprout is about 

 40, and the highest about 103. The lowest for corn 

 and squashes is about 50, and the highest about 115. 



Although the seeds may sprout at any point within 

 this range of temperature, at a point near either extreme 

 growth will be very slow, and the plants weak and small. 

 There is a certain degree of heat for each variety of 

 seeds in which they will produce the best growth. That 

 point for wheat, oats, and barley is about 84, and for 

 corn and squashes about 94. The nearer we approach 

 to this favorable point in choosing the land and the 

 time for planting, the better the results. The mistake 

 is often made of planting seeds too early in the spring, 

 before the ground is sufficiently warm to insure quick 

 and strong growth. ' The early plant is so weakened 

 by low temperature as to gain nothing in the end over 

 the later plant, which thrives better, and yields larger 

 results. 



3. Oxygen. Oxygen, which is essential to support 

 life in animals, being taken into their systems through 

 the air in their lungs, is also essential to the life and 



