22 Elementary Principles of Agriculture 



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 rapid 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. 



The table below shows the effect on the time in 

 coming up, of planting wheat at different depths, and 

 the number of seedlings that grew. 



Proportion of seed 

 Depth Time in comtn? up that grew 



% inch 11 days f 



1 inch 12 days all 



2 inches 18 days $ 



3 inches 20 days f 



4 inches 21 days 



5 inches 22 days f 



6 inches 23 days ^ 



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. 



