Germination. 25 



suiiies its active state, and the cells of a certain part of 

 the seed begin to increase in size and to divide (15), 

 causing the tiny shoot to burst through the seed-case. 

 Germination is completed when the young plant (plant- 

 let) is sufficiently developed to live without further aid 

 from the seed. 



29. Moisture is Essential to Germination. Air-dry 

 corn or other seeds will not germinate if kept however 

 long in a warm room, whereas viable seeds, that have 

 absorbed water until fully swollen, will usually germi- 

 nate if exposed to air of a suitable temperature, under 

 conditions that prevent their loss of moisture. This 

 shows that a certain amount of moisture must be absorbed 

 by the seed before germination can take place. Seeds 

 must be nearly or quite saturated with water before they 

 will germinate. 



In culture we plant seeds in some moist medium, usu- 

 ally the soil, in order that they may absorb moisture and 

 germinate, and thus develop into new plants. 



30. Warmth is Essential to Germination. Had we placed 

 the seed-tester mentioned in paragraph 28 in a refrigera- 

 tor in which the temperature never rises above 46 F., 

 instead of in a warm room, the corn grains would not 

 have germinated however long they remained there. 

 This shows that a certain degree of warmth is also nec- 

 essary to germination. Without this, the protoplasm ot 

 the seed cannot assume its active state (13). The low- 

 est (minimum) temperature at which seeds can germi- 

 nate varies considerably with different species, and so 

 does the temperature at which they germinate soonest 

 (optimum) as also the highest (maximum) temperature 



