Page:Life Movements in Plants.djvu/194

164 Calculating from the data obtained from the figure we find :—

The absolute value of the normal rate ... 0'457/i. per second.

Diminished rate under cold ... ... 0"101/a „ „

Enlianced rate uruler warmth ... ... iSlfx, ,, ,,

Moving 2)late method : Experiment 54. — This was carried oat with a different specimen of S, Kysoor, the record being taken on a moving plate (Fig. 596). The first part of the curve here represents the normal rate of growth. The plant was then subjected to moderate cooling, the sub- sequent curve with its diminished slope denotes the depres- sion of growth. The question of influence of temperature will be treated in a subsequent Paper of the present series in much greater detail.

Precaution against piiysical disturbance : Experiment 54 There may be some misgiving about the employment of such high magnification : it may be thought that the accuracy of the record might be vitiated by physical disturbance, such as vibration. In physical experimenta- tion far greater difficulties have, however, been overcome, and the problem of securing freedom from vibration is not at all formidable. The whole apparatus need only be placed on a heavy bracket screwed on the wall to ensure against mechnical disturbance. The extent to which this has been realized will be found from the inspection of the first part of the record in figure 60, taken on a moving plate. A thin dead twig was substituted for the growing plant, and the perfectly horizontal record not only demon- strated the absence of growth movement but also of all disturbance. There is an element of physical change, against which precautions have to be taken in experiments on varia- tion of the rate of growth at different temperatures. In order to determine its character and extent, a record was taken with the dead twig, of the effect of raising the temper- ature of the plant-chamber through ten degrees. The record