ME. F. DAEWIN ON LEAVES WITH EEGAED TO LIGHT. 451 



spindle of the klinostat, the other on the arbor of one of the clock- 

 wheels. This principle has several advantages. The spindle can 

 be instantly put out of gear by slackening the silk ; the plant 

 under observation can be at once removed without interfering 

 with the clockwork. Another good point in the construction of» 

 the klinostat is that the plant is fixed to the free end of the 

 spindle, which projects beyond the bearings, instead of in the 

 middle; the shading* of the plants, which occurs if the plants 

 are fixed to the middle of the spindle, can thus be avoided. As 

 the plant is connected with the motive power by a spindle (Jc, 

 fig. 13) only a centimeter in diameter, it can be covered with a 

 properly constructed glass case, by which the air in its neighbour- 

 hood can be kept damp, while the clockwork will be in the dry 

 air of the room. By means of a like arrangement I have kept 

 the klinostat going for many weeks out of doors, the clock- 

 work being in a box, the plant exposed to the open air. But 

 the special advantage of my brother's design is the device by 

 which the centre of gravity of the plant can be made to coin- 

 cide with the axis of rotation of the machine, so that a very con- 

 siderable weight can be easily driven by the clock. The box in 

 which the plants are grown, or in which a flower-pot may be 

 easily fixed, is shown at B (fig. 13). By means of a thumb-screw 

 th the box can be attached to the wooden plate pi, which in its 

 turn is fixed to the strong steel spindle (10 millim. diameter) #, 

 which forms the axis of rotation of the machine. The box is a 

 cube, and can therefore be fixed in two positions, so that the 

 axis of the plant may be either parallel or perpendicular to the axis 

 of rotation (see fig. 17). The spindle k turns at one end in a hole 

 in a piece of brass plate at the upper end of the wooden pillar or 

 support s. The other point of support of the spindle is supplied 

 by the brass friction-roller fr, which turns in a simple slot in the 

 wooden supports, the spindle being grooved aty to fit the wheel. 

 The two supports s and s are fixed, 255 centim. apart, in the 

 wooden board b b, 40 centims. long. The board b b projects 

 beyond the support * to give room for a heavy weight wt, 

 which may be used to counterbalance the weight of the plant if 

 required. The driving-force is supplied by a common American 

 watch-action clock c, on one of whose smaller wheel-arbors a 

 grooved pulley^ is fixed. The pulley on the clock being then con- 



* Sachs, loc. cit. p. 220. 

 LINN. JOUEN. — BOTANY, VOL. XVIII. 2 L 



