246 Darwin and Pertz . — On the Production 
which the sporangium was carried round in a circle, like the 
free end of a circumnutating organ. Elfving’s interesting 
paper 1 on the growth of the pulvini of grass-halms on the 
klinostat proves that the geotropic stimulus may in like 
manner be continuously felt 2 . It is clear that in some cases 
the plant is not strictly speaking freed from external stimuli, 
although no permanent curvatures are produced. 
It was to obviate this difficulty that the intermittent 
klinostat was devised and made for us, at the Cambridge 
Scientific Instrument Company’s works, by Mr. H. Darwin. 
Round the horizontal spindle of a klinostat 3 a cord is 
wound, which passes over a pulley and is attached to a weight. 
If the weight is allowed to descend the spindle will rotate, and 
it is this arrangement which gives the motive power to the 
instrument. The weight, however, is not allowed to act con- 
tinuously : by means of a clock-work escapement, the spindle 
is only permitted to make a half-revolution twice in every 
hour. A simple but efficient fan-governor is fitted to the 
spindle, and the rotation is thus rendered so gentle, that no 
harmful jar is communicated to the plant. 
If we imagine a plant attached to the klinostat, it is clear 
that it will, during the first half-hour, receive a geotropic 
stimulus tending to make it curve in a certain direction, and 
that during the next half hour an equal and opposite stimulus 
will tend to undo the effect produced in the first period. 
Under this series of stimuli, an ordinary apogeotropic shoot 
remains approximately straight, exhibiting however a rhythm 
of slight curvatures in the vertical plane which will be here 
described. The first use that we made of the instrument was 
to investigate rectipetality. Vochting has shown that an 
organ which has been allowed to curve geo- or heliotropically 
and is then cultivated on the ordinary klinostat, loses the 
bend and becomes straight. This power of accommodation 
1 Ueber das Verhalten d. Grasknoten am Klinostat. 
' z Schwartz’s experiments on growth during slow rotation point to an opposite 
conclusion. See Untersuch. Bot. Inst. Tubingen, I, 1881. 
3 We use the pattern of klinostat described by one of us in the Linnean 
Society’s Journal, 1881, vol. xviii. 
