438 PHYSIOLOGY OF GROWTH. 



and its ends are pierced with numerous small holes, to promote the 

 ventilation of the soil contained in the box. We use light, very 

 humous soil such as is employed for greenhouse plants, moisten 

 it with water, not however adding too much to prevent its 

 being crumbled between the hands, and then pass it through a 

 sieve with meshes 1'5 mm. wide. In filling the box the soil must 

 not be pressed down ; it must be loosely packed, so that the 

 development of the roots may go on smoothly. The requisite seed- 

 lings have been cultivated, as above described, in moist sawdust. 

 We take the plants when their roots have attained a length of 

 a few mm. First we must make fine ink lines on the roots to 

 serve as marks. We dry the roots carefully with a piece of linen, 



FIG. 141. Zinc case v>ith glass walls for observations on 

 root development. 



and then make the ink -marks, at intervals of 2 mm., with a 

 sable pencil. This operation, which must be carefully performed, 

 is best managed with the help of a large smooth sheet of cork 

 about 2 cm. thick, on the left side of which a number of large 

 notches of different sizes are made with a round file, from which, 

 along the surface of the cork, pass grooves made with a thin 

 round file. In ( the notches are placed the seeds ; the grooves 

 receive the roots, and alongside them is placed a millimetre scale. 

 The seedlings when ready are placed in the soil of our box, with 

 their roots directed horizontally and closely applied to one of the 

 glass faces, loosely covered with soil, and observed. We fasten 

 on the outside off the glass a small triangular piece of paper, of 



