THE A WAKENING OF THE SEED 



39 



top is reached. The box should then be filled with 

 earth and the last row of seeds planted on the top. 



The soil should be kept moderately moist and 

 at a temperature favorable to germination. The seeds 

 are now under approximately the same conditions as 

 exist in the soil; as we go deeper we find more water, 

 less air (and less circulation of air) and less warmth 

 (in our apparatus the lower layers of soil are apt to be 

 warmer than is naturally the case). Our experiment 

 indicates that there is a certain depth where the three 

 needs of the germinating seed are best provided for. 



Various mechanical devices are in use for planting 

 seeds at uniform depths in the soil (e. g., corn-plant- 



34. Apparatus for determining how deep seeds sliould be planted 



