Page:Life Movements in Plants.djvu/264

234 wheel in the clockwork connected with an eccentric is released periodically, at intervals which may be varied between one and five seconds. ly the action of the eccen- tric, the plate carrier approaches the writing levor with diminishing speed till the movement is zero at the .contact. This contrivanco is essential, since any sudden shock of the plate against the lever is apt to give rise to after-vibra- tions of the writer. The plate carrier is quickly with- drawn after the production of a dot on the smoked glass plate by contact with the writing lever.

’l‘ho elookwork is governed by a revolving 'fan which
 * an be gradually opened out by a regulating screw. The

speed ean thus be adjusted within wide. limits, and main- tained constant and at any desired speed. A second set of wheels connected with the clockwork moves the plate-holder in a lateral direction. A series of records may thus be taken for fifteen minutes, half an hour, or an hour.

The record obtained in this way is very perfect. Not only is the. Mind of an external agent shown by variation in the amplitude and frequency of pulsations, but the change of speed in any phase of the pulse becomes auto- matically recorded.

The whole plant. am not b.- conveniently manipulated for different investigations. It is, however, possible using the precautions described below to use the. detached petiole carrying the pulsating leaﬂets. The terminal large leaf may also be removed. The necessary amputation is often followed by an arrest of pulsation. But as in the case of isolated heart in a state of standstill, the movement of the leaﬂet may be revived by the application of internal hydrostatic pressure. Under these conditions, the rhythmic pulsations may easily be maintained uniform for many hours.