Growth. 1 7 



the dicotyledonous stem, which is monostelic. Every stele in 

 the internode accomplishes a definite amount of growth during 

 a short period, and then forms the heavy stereome which marks 

 the end of increase both in length and thickness. This fact 

 will explain the varying thickness of the different internodes of 

 the stem and also the non-formation of bark in such plants. 



6. Measurement of growth in length by auxa- 

 nometers. Increase in length of the stem is more or less 

 continuous during the vegetative season, but the rate of such 

 increase is not easily calculated by the unaided eye. If the 

 tip of the growing organ is attached to the short arm of a lever 

 in such manner that the comparatively slow motion of the 

 growing parts will cause a magnified movement of the long arm 

 of the lever, a fairly accurate estimate may be made of the rate 

 of elongation. Auxanometers, or devices for measuring growth, 

 may be set up as follows : 



Make a smooth hole, half of the length of a cylindrical cork, 

 with a diameter of about three centimeters, and fit it to the top 

 of the upright rod of a retort stand. Drive four pins in the 

 top of the cork in such manner as to make two parallel X's. 

 Secure a splint of light wood about seventy-five or eighty cen- 

 timeters long, and attach a thread of slightly greater length to 

 each end. Fasten a small piece of wood to the strip at right 

 angles to it, and pass the cord over the top of the strip in such 

 manner that a bracing effect is obtained that gives additional 

 rigidity to the strip. Measure the strip of wood into two parts, 

 in the ratio of one to twenty-five, and drive a pin through the di- 

 viding point. Suspend the lever thus formed in the bearings 

 made by the crossed pins on the cork, and fasten pieces of 

 lead to the short arm of the lever until it is nearly as heavy as 

 the long arm. The length of the long arm may be increased 

 by fastening a bristle to its end with glue, and in all instances 

 the effort should be made to increase the ratio between the 

 length of the arms with the greatest possible lightness. Secure 



