182 MINNESOTA BOTANICAL STUDIES. 



constructed of aluminum, it can be used on plants while they 

 are under normal conditions of moisture, without injury to the 

 instrument. The auxanometer proper can be separated an in- 

 definite distance from the registering apparatus. Registrations 

 have already been made in the laboratory of the growth of 

 plants under natural conditions, 400 yards distant and in 

 another building. 



The auxanometer consists of a ratchet-wheel on a steel 

 axis which also bsars a series of smiU grooved wheels 1, 

 3i and 6 mm. in diameter, and a somewhat larger wheel 

 upon which is wound a thread bearing a counter-weight. The 

 diameter of the larger wheel, is about 5 cm. and the circum- 

 ference contains 144 notches. A ratchet which fits in the 

 notches of this wheel, is mounted on an axis similar to that of 

 the others, and has a long horizontal arm. This arm has a 

 platinum tip. As the large wheel turns, the ratchet drops 

 into the notches in its circumference and the platinum tip is 

 lowered so that it touches a drop of mercury which is held in 

 a small cup on the arm of the frame. This arm is insulated 

 from the rest of the instrument and is connected by means of a 

 small wire, to one pole of an electric battery. The other part 

 of the instrument is connected with the other pole of the 

 battery. The screw underneath enables the height of the 

 mercury to be regulated, and consequently the length of time 

 which the current remains closed or open. 



The frame work of the instrument is made of aluminum, 

 and entire weighs 15 gms. It may be attached to the arm of a 

 tripod support, and in this position can be used for measuring 

 growth in length, (as shown in Plate x). For measuring growth 

 in thickness the instrument can be fastened to the support and 

 held against the stem, or fruit, which is to be measured, or it 

 can be removed from the support and attached to the plant. 

 When attached directly it is held in place by a clamp. This 

 can be entirely removed and placed around the plant. It is 

 roughly adjusted in place by means of a catch, which fits into 

 the notches on the clamp. The fine adjustment is ac- 

 complished by a screw. When the apparatus is in place a silk 

 thread is fastened to the hook on the frame, passed around 

 the plant in the direction opposite the hands of a clock, so 

 that the thread may be in contact with the entire circumference 

 of the plant. The thread is then passed through a hole in the 

 axis of the auxanometer where it is securely fastened and the 



