268 MR. F, DARWIN ON A METHOD OF INVESTIGATING THE 
Various attempts were made to support the weight of the 
cotyledons, and some success was obtained with a vertical wheel 
by means of which the counter-weighted cotyledon could rotate, 
the tip of the root being fixed at a point opposite the centre of 
rotation. But the apparatus finally adopted was one suggested 
by my brother, Mr. H. Darwin, and made for me by the Cam- 
bridge Scientific Instrument Co. 
A wooden lever 53 em. in length (L in fig. 4) turns on a 
knife-edge K, fixed about 7 cm. from one end; the meial bearing 
M, on which K turns in the vertical plane, is able to rotate in 
the horizontal plane by means of a supporting-rod fitting into 
the vertical tube T. 
Fig. 4. 
L, the lever; K, the knife-edge; M, its bearing; T, bearing for vertical rod 
(not shown); W, the counter-weight; P, the pin supporting B, the bean > 
C, a second counter-weight. 
The cotyledons of the bean B are fixed to the lever by a pin P 
on which B can rotate in a vertical plane, and the weight of the 
bean is counterbalanced by the lead block W, the balance being 
finally adjusted by the counter-weight C,a ring of lead wire 
which slides on the lever L. By this arrangement the cotyledons 
can move freely in any direction on the surface of the spbere of 
radius PK (46em.). Fig.5 gives a view from the point Pin 
g. 4e 
Fig. 5. 
T, the tube in which the tip of R, the radicle, is fixed ; L, the lever. 
The square L is the lever seen in section, and the dot, in the 
middle is the head of the pin P; L would, as a fact, be invisible. 
being hidden by the bean B. 
