GROWTH OF THE BODY 



283 



thread held taut by means of a pair of calipers, or bow of wire. 

 Apply the ink to the thread with a camels hair brush, and mark 

 the root as delicately as possible. Fit a cork to a glass cylinder 

 6 cm. in diameter and 20 cm. in height, and fasten the seedlings 

 to the lower side of this cork in such manner that the roots will 

 depend vertically near enough to the sides of the cylinder, to 

 come within the focus of a horizontal microscope. To fasten the 

 seedlings, bore holes the size of the main axis of the seedlings in 

 small corks, and then split the corks. Clamp them lightly around 

 the plantlet and hold together by 

 two short pins driven through the 

 halves, using a third pin to fasten 

 the whole to the stopper. After the 

 seedlings are in place, use the hori- 

 zontal microscope with ocular mi- 

 crometer and measure intervals on 

 roots exactly (Fig. 134). 



Pour some water in the bottom 

 of the cylinder and set in a dark 

 room at a temperature of about 20° 

 C. Measure the distances between 

 the ink lines again in 12, 24, 48 and 

 72 hours, and note region of great- 

 est growth, keeping record of the 

 accretions. Plot curve showing the 

 amount of growth in the regions beginning at the tip, and compare 

 with data obtained from measurements of elongations of cortical 

 cells. 1 



363. Growth of the Body. The multiplication of cells in gen- 

 erative layers, and the constant differentiation of the greater num- 

 ber of these to permanent tissues adds to the bulk of the frame- 

 work of the organism, an increase which continues during the 

 entire lifetime of the plant, broken of course, by the seasonal 



1 The daily periodicity and total growth of the root may be recorded by means of 

 an apparatus described by Dr. G. E. Stone, in the Botanical Gazette, 22 : 261. 1896. 



A B C 



Fig. 134. Demonstration of region 

 of growth in roots. A, showing 

 method of preparation of seedling. 

 B, showing relative position of marks 

 on apical portion of root at begin- 

 ning of experiment. C, position of 

 marks a few hours later. 



