38 mXPMBIMENTS WITH PLAXTS 



packed in the bottle at first. The natural condition 

 of the soil could be more closely simulated by 

 forcing a tin cylinder (a tin can with the bottom 

 removed would do) into the soil (using a rotary mo- 

 tion), measuring the cylinder of soil so obtained and 

 pouring it slowly and cai'efully into an equal bulk 

 of water. 



The deeper the seed lies in the soil, the less will 

 be the circulation of air about it. A constant renewal 

 of air is necessary, as we have already learned. The 

 question naturally comes up. How does the depth at 

 which the seed is buried affect germination ? One way 

 of finding out is by means of a box, with one side 

 of glass, in which seeds may be planted at different 

 depths, as shown in Fig. 34. A convenient way of 

 making such a box is to prepare the sides (as shown 

 in the figure) and then make saw cuts in them to 

 receive the glass, which is then easily removed when- 

 ever necessary. A wooden strip for the bottom and 

 another for the side (to give rigidity) complete the box. 

 Both sides may be of glass, or one of glass and the 

 other of wood. A box an inch wide at the top, with 

 sides a foot square, is of very convenient size. The 

 joints may be made air-tight by means of putty. 

 In planting the seeds, the box should be tilted and 

 a row of seeds placed directly on the glass; earth 

 should then be pressed down on them; another row 

 of seeds should then be planted, and so on until the 



