MOVEMENTS OF GROWTH. 



383 



bed. Care must be taken that the emerging roots will not have to 

 make curvatures in order to grow vertically downwards. The Vicia 

 seeds we lay in the sawdust with the micropyle directed down- 

 wards. The Phaseolus seeds are laid horizontally, so that the 

 emerging main root forms a right angle with the long axis of the 

 seed. When the roots have attained a length of To-2 cm., the 

 seedlings are removed from the bed, carefully washed, dried with 

 a piece of soft linen, and provided with marks. We use the best 

 black Indian ink, rub it with a little water on a porcelain plate, and 

 paint fine lines on the roots with a sable pencil. The distance be- 

 tween the marks may be 1, 1/5, or 2 mm., according to circum- 

 stances. The first line is therefore 1, 1'5, or 2 mm. distant from 

 the growing point,* the second 1, 1/5, or 2 mm. from the first, 

 and so forth. It is best to take distances of 1 mm. In marking the 

 roots it is convenient to proceed as follows : We take a sheet of 

 cork, say 2 cm. thick, along the left edge of which a number of 

 large notches have been made with a r6und file; from each of 

 these, along the surface of the cork, run in 

 different directions a few grooves made 

 with thin round files. We now find a 

 notch in which the seed with a little 

 coaxing will stick, its root at the same time 

 lying in one of the grooves. Alongside 

 the root we lay a millimetre scale, in such 

 a way that we can draw the lines on it as 

 continuations of the divisions of the scale. 

 The seedlings, whose roots have been 

 marked, are now fixed in glass cylinders 

 by means of long pins in the manner in- 

 dicated in Fig. 126. I used cylinders about 

 30 cm. in height, and 7-8 cm. in diameter, 

 and also much larger ones, which are 

 preferable. The cork, K, into which the 

 pins are stuck, is cemented on the bottom of --^ ^^ 



f. ... FIG. 126. Glass cylinder 



tlie stopper with sealing-wax, and is soaked for culture of seedlings. 

 with water. The bottom of each cylinder 



is covered with a layer of water, so that the roots are surrounded 

 by moist air. If it appears to be necessary, we may further sprinkle 



* The growing point is of course only seen indistinctly glimmenng through ; 

 it is situated about 0-2-0-5 mm. from the root tip. 



