22 Elementary Principles of Agriculture 



orous-growing weeds may crowd out slow-growing seed- 

 lings. Prompt germination may be secured under field 

 conditions by thoroughly preparing the seed bed, and 

 delaying planting until the soil is warmed sufficiently 

 for the kind of seed to be planted. (See U 27.) 



35. Time Required to Complete Germination. The 

 plantlets are nourished for a time by the reserve food 

 in the seed. While the plantlet is dependent on this 

 reserve food, it is called a "seedling." The root develops 

 faster at first, with the result that the plantlet secures 

 a more permanent supply of moisture from the deeper 

 layers. The roots grow down or downward, and the 

 stem and leaves grow upward into the air. The time 

 required for the completion of the seedling stage will 

 vary with the kind of seed and the conditions which 

 affect germination. When conditions favor quick ger- 

 mination and rapfd growth, the supply of reserve food 

 is used up much sooner. Wheat seedlings will exhaust 

 their reserve food in ten days in warm weather; but, if 

 the temperature is low, it may be forty days before the 

 plantlet is thoroughly established. 



36. Hotbeds. It is often desirable to grow seedlings 

 under artificial conditions, so that the plants may be 

 ready for transplanting when the warm season comes. 

 Many tender garden plants, such as tomatoes -and cab- 

 bages, are propagated in this way. Coldframes and hot- 

 beds are often used A coldframe is an inclosed bed of 

 soil that may be covered at night to protect from frost. 

 A. hotbed is an inclosed bed of soil, covered with glass, 

 as shown in Fig. 19, which is warmed by the heat of 

 fermenting compost placed below the bed of soil. Some- 

 times steam pipes are run below the seed-bed to supply 

 the warmth. 



