304 - BOTANICAL GAZETTE [ocropER — 
a height that it may be wound and regulated from beneath without disturb- 
ing the record. The magnifying wheel, really four concentric wheels 
combined, allows three degrees of magnification, two, four, and eight times 
the actual growth. It is made of aluminum, moves on a very sensitive axle, 
has suitable openings for attachment of threads, and is provided with a 
clamp for holding it immovable while adjustment of threads and the like 
is being made. The tip of the plant is brought into action with the wheel 
by means of a fine thread in the usual way; but in order that this thread 
may be kept as short as possible, a plant support, adjustable for height, is 
provided on a separate rod, thus permitting the tip of the plant to be kept 
close to the magnifying wheel, though, of course, care must be taken to 
prevent the danger of shading, and hence of phototropic bendings. This 
adjustable support, however, has another very important use which will 
be mentioned below. The thread from the large wheel passes over a _ 
pulley to the pen carrier, which slides on a fine guide wire and has sufficient 
weight to turn the wheels in proportion as the growth of the plant permits 
the small wheel to turn. The pen is of glass, drawn to a capillary point 
and bent so as to rest at right angles to the paper. It is filled with chrono- 
graph ink, and, as the plant grows and the cylinder turns, it traces a fine 
spiral line down the cylinder, crossing any given vertical line once an hour. 
When this pen has reached the bottom of the cylinder, one has only to 
put on a new cylinder or record paper, turn the large wheel backward until 
the pen is drawn to its top, close the clamp to hold the wheel immovable, 
lower the plant support until the, thread from the plant becomes again 
taut, loosen the clamp to allow the tensions to adjust themselves, and then 
the record is resumed; and this procedure can be repeated until the end of 
the experiment without any need for ever touching the threads. This is 
the other advantage, above mentioned, of the adjustable plant-suppott. 
One should never draw up the pen by lowering the plant support, as there — 
is a constant temptation to do, since this brings an unnatural strain upon 
the plant tip. All parts of the instrument, even to the arms carrying 
magnifying wheel and pulley, are adjustable, so the instrument may be 
made to work smoothly under any conditions. While designed primarily 
for making records of growth, it can be used for any measurements involy- 
ing movement, e. g., the rise of water in a tube. 
The weak point of all auxographs lies in the threads, which will alter 
length hygroscopically and thus introduce error into the record, despite 
any known treatment with wax, oil, rubber, etc. These alterations may be 
minimized by treating the threads with wax, and by keeping them as short 
as possible, for which reason they should be made only long enough to 
