202 PLANT PHYSIOLOGY 



can be seen from a considerable distance. Its construction is shown by 

 the accompanying figure (Fig. 55). A wooden base, with handles for trans- 

 port and screws for levelling, carries an attached framework which sup- 

 ports the magnifying wheel, recording cylinder, and clockwork, the latter 

 being fastened to a tripod high enough to allow it to be wound and regulated 

 from beneath. The clock is a Waterbury alarmless (costing one dollar), 

 with all surplus parts removed, leaving the steel spindle, which turns once 

 an hour, projecting above the works; these are protected from dust by 

 tight-fitting cardboard pieces resting on the frame of the works. The record 

 cylinder, 2.5X30 cm., is turned from hard wood, with a hole at one end for 

 the spindle (a small pin projecting down between the cogs on the spindle 

 will make it revolve with the latter) and a hole at the other for a pin to hold 

 it upright. The cylinder is covered with paper — preferably cross-section 

 paper ruled in millimeters — put on tightly and gummed by one edge, which 

 overlaps the other in a direction such that the pen will not catch upon it. 

 The magnifying wheel contains in one piece four concentric wheels, respec- 

 tively 1.5, 3, 6, 12 cm. in diameter (to bottoms of their grooved rims), and 

 a small hole through the axis allows it to be supported by a pin held in a 

 needle-holder. It should turn freely, come to rest in any position, and be 

 coated lightly with shellac to prevent warping. There should be provided 

 a spring clamp to hold it still while the experiment is being started. The 

 pen is made from small glass tubing drawn to a capillary point and bent at 

 right angles, as shown by the figure, the point being smoothed by rubbing 

 gently on a piece of ground glass. It is filled with chronograph ink (drawn 

 into it by suction), and supported in a holder made from a brass paper- 

 fastener. This holder has a small hole through which passes a guide-wire 

 running from the frame above to the works below, thus preventing the pen 

 from becoming jarred away from the cylinder. The combined weight of 

 pen and holder should be just great enough to tum the magnifying wheel 

 with certainty. The plant being placed in position with the wheel clamped, 

 a thoroughly waxed fine silk thread is tied in a loose loop just under the 

 tip of the stem, is run once around the smallest wheel (for greatest magnifi- 

 cation), and fastened in a nick in the wood. Another waxed thread is then 

 attached to the penholder, is run over a small pulley-wheel on the frame, 

 is turned twice around the largest wheel, and is fastened. The whole 

 arrangement is such that when the wheel-clamp is released the pen 

 will start at the top of the cylinder and descend as the plant grows, 

 tracing a record, which, owing to the hourly revolution of the cylinder, 

 will be a spiral line crossing any given vertical line once an hour. 

 A lesser magnification is given, of course, by use of the other wheels. 

 It is best to have two cylinders, so that a fresh record paper may le 

 substituted without delay. The record papers may be preserved either 

 as cylinders, or, better, flattened and attached to a board, in which 

 latter case it is easy to rule lines to show not only the hourly, but even 

 lesser periods of growth. This apparatus has, incidentally, the advantage 

 that it may be applied also to other measurements involving rise or fall of 

 an object, of a water-level, etc. 



