CELLULAR ANATOMY OF THE STEM 225 



and through the common axis of both a fine, smooth hole 

 is turned by which the wheel will revolve with very little 

 friction on a clean new needle fixed horizontally by solder 

 or sealing-wax to a firm horizontal support. From the very 

 tip of the stem to be studied a fine silk thread, thoroughly 

 waxed to prevent absorption of moisture, is to be run several 

 times around the small wheel to which its end is fastened 

 by a small drop of glue. A similar thread is to be run 

 around the large wheel and fastened, while the free end 

 carries a pen pressing against a paper on the cylinder. This 

 paper should be smooth, put on the cylinder while mois- 

 tened, and gummed by the free edge, so that when dry it 

 will fit without wrinkles. The pen is to be made from a small 

 piece of slender glass tubing bent into a curve so that both 

 ends, carefully smoothed, rest against the paper ; but one of 

 them is drawn into a capillary point and bent and filed so 

 it rests at right angles to the paper. A chronograph ink 

 should be placed in this pen, on which weight enough should 

 be placed to make the wheel turn as the plant grows. As the 

 plant grows the pen will descend, marking a spiral line on the 

 paper, and the distance apart of the spirals where they cross 

 any given vertical line will give the exact amount of growth 

 per hour, magnified, of course, just in proportion to the rela- 

 tive sizes of the wheels. Half-hour periods may be found by 

 ruling two vertical lines at 180 apart, and then removing the 

 paper on one side between them, bringing the vertical lines 

 together. Of course, the paper with the record may be re- 

 moved from the cylinder for preservation. 



Rapidly growing flower stalks of such plants as Hyacinth 

 are very good for this purpose, but any parts that are growing 

 vertically may be used. Variations in temperature can easily 

 be effected where there is a Wardian case ; or even by leav- 



Q 



