106 The Botanical Gazette. [April, 
wire that serves asa pen. The end of the wire or pen is ham- 
mered out very thin, and cut with a pair of scissors to a deli- 
cate point. A length of one or two cm. near the base is also 
flattened to lessen the rigidity of the wire, that the point may 
offer much less resistance when in contact with the cylinder. 
It is necessary that the pen should be long and sufficiently 
curved, so that the straw itself does not come in contact with 
the cylinder. 
To the other balance arm the plant is connected by meafs 
of a thread fastened to the under side of the scale. Before at 
taching the plant, however, enough weight is added to the 
left hand scale to balance the weight of the straw, after which 
a small weight (in our experiments .04 gm.) is added to the 
right hand scale to produce the proper deflection, which should 
be equal to at least one-half the length of the registering cyl 
inder. The amount of deflection can be determined by 4 
paper protractor fastened at the top of the balance. If now 
we have a deflection equal to one-half the length of the resi 
tering cylinder, and the balance arm be placed at a comes 
ponding point above the horizontal position, the pen will have 
an amplitude of motion equal to the whole length of the cy 
inder. When the balance arm is in this latter position the 
plant is attached, and it is evident now that the tension the 
thread would not be .04 gm., but .o8 gm. It is esirable 
that the straw and pen should be exceedingly light, ° nee 
unimportant with such smallweights. The original apparatis’ 
of 
quired a weight or tension of 20 gm.; that Wiest’ 
of 7 to 10 gm.; and the apparatus used by Pfeffer, eve? i 
compensated as fine as possible, must have a tension of 1.59% 
in general, however, this apparatus is used with a tens 
to IO gm. 
ae a a well known fact that even a tension of a few ge 
ects the normal growth of a plant; notwithstanding : 
: 
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