16 Elementary Principles of Agriculture 



down firmly on one end and leave loose on the other. Cover with 

 a glass, to prevent drying out, and note the time required for ger- 

 mination in the two ends. 



25. Other Conditions affecting the rate of absorption 

 of water by the seeds, are temperature, the nature 

 of the seed-coat, etc. The seed covering of most culti- 

 vated plants will absorb and transmit the soil-water 

 quite freely, though many seeds are provided with thick, 

 bony shells, or coats, that resist the action of water for 

 weeks, even months, if they once become dry. Such 

 seeds are the peach, locust, walnut, and most wild 

 seeds. Germination may sometimes be hastened in 

 such seeds by soaking in warm water before planting; 

 freezing while moist aids and hastens others, especially 

 those having thick, hard shells, such as peach, walnut, 

 hickory, plum, etc. 



26. How Warmth Affects Germination. A certain 

 degree of warmth is necessary before seeds will germi- 

 nate. If we had placed in a refrigerator the seeds used 

 in the experiment described in H 15, the corn and 

 beans would not have germinated, although they 

 had plenty of water and air. This shows that a certain 

 amount of warmth is necessary for germination. Some 

 seeds, however, will germinate at a very low temperature, 

 though they do not germinate quickly. The lowest 

 temperature at which seeds will germinate is called 

 the " minimum germination temperature." The high- 

 est temperature at which they can germinate and live 

 is called the " maximum germination temperature." 

 Between the highest and the lowest there is a temperature 

 at which germination takes place quickly, but without 

 injury to the seedlings. This is called the " optimum 

 germination temperature." These temperatures have 



