Page:Life Movements in Plants.djvu/201

Rh growth was found to be .3 metres in ﬁve seconds, or 60 cm. per second. This is a million times the actual rate of growth of the (Yrinum bud. As it. is easy to measure 5 mm. in the scale, it will be seen that. with the Demonstration Crescograph it is possible to detect the growth of a plant for a period shorter than a hundredth part of a second.

Experiment 57.——A scale 3 metres long divided into cm. is placed against the screen. A metronome beating half seconds is started at the moment when the spot of light transits across the zero division; the number of heats is counted till the index traverses the 300 cm. At the normal temperature of the room (30 (-1.), the index traversed 300 cm. in live seconds. The plant chamber was next cooled to 2690. by the blowing in of cooled water vapour; the time taken by the spot of light to traverse the scale was now 20 seconds, 17.0., the growth- rate was depressed to a fourth. Under Continuous lower- ing of temperature the growth-rate became sloWed down till at 2100. there was an arrest of growth. Warm vapour was next introluced, gradually raising the tempera- ture of the chamber to 35%}. The spot. of light new rushed across the scale in a second and a half, 210., the growth was enhanced to more than three times the normal rate. The entire series of the above experiments, on the effect of temperature on growth, was thus complet- ed in the course of 15 minutes.

A description is given of the High Magnification Crescograph, which enables an automatic record elf growth magniﬁed ten thousand times. The absolute rate of growth can be easily determined from the data given in the record.