Fig. 59.—Crescographic records: (A) successive records of growth at intervals of one second (magnification 10,000 times). (a) Effect of temperature on a stationary plate; N, normal rate of growth; C, retarded rate under cold; H, enhanced rate under warmth; (b) record on moving plate, where diminished slope of curve denotes retarded rate under cold (Magnification 2,000 times.)
After the completion of the first vertical series, the recording plate was moved 1 cm. to the left; the tip of the recorder was brought once more to the top by the micrometer screw, S, ([Fig. 58]), and the record taken once more after an interval of 15 minutes. The magnified growth for 4 seconds is 38 mm. in the first record; it is precisely the same in the record taken fifteen minutes after. The successive growth elongations at intervals of 1 second is practically the same throughout, being 9.5 mm. This uniformity in the spacings demonstrates not only the regularity of growth under constant conditions, but also the precision of the apparatus. It also shows that by keeping the external condition constant, the normal growth-rate could be maintained uniform for at least fifteen minutes. The magnified rate of growth is nearly 1 cm. per second, and since it is quite easy to measure 0.5 mm. the Crescograph enables us to magnify and record a length of 0.0005 mm. that is to say, the sixteenth part of a wave of red light. The absolute rate of growth, moreover, can be determined in a period as short as 0.05 of a second. These facts will give some idea of the great possibilities of the Crescograph for future investigations.
As the period of experiment is very greatly shortened by the method of high magnification, I shall, in the determination of the absolute rate of growth, adopt a second as the unit of time, and µ, or micron, as the unit of length,—the micron, being a millionth part of a metre or a thousandth part of a millimeter.
If m be the magnifying power of the compound lever and l, the average distance between successive dots in mm. at intervals of t seconds then:—
the rate of growth = l/mt × 103µ per second.
In the record given l = 9.5 mm.
m = 10,000.
t = 1 second.
Hence the rate of growth = 9 .5/10,000 × 103µ per sec.
= 0.95µ per sec.
Having demonstrated the extreme sensitiveness and reliability of the apparatus, in quantitative determination, I shall next proceed to show its wide applicability for various researches relating to the influence of external agencies in modification of growth. For this two different methods are employed. In the first of these methods, the records are taken on a stationary plate: of these the record is at first taken under normal condition, the subsequent series being obtained under the given changed condition; the increase or diminution of intervals between successive dots, in the two series, at once demonstrates the stimulating or depressing nature of the changed condition.
In the second method, the record is taken on a plate moving at an uniform rate by clockwork. A curve is thus obtained, the ordinate representing growth elongation and the abscissa the time. The increment of length divided by the increment of time gives the absolute rate of growth at any part of the curve. As long as the growth is uniform, so long the slope of the curve remains constant. If a stimulating agency enhances the rate of growth, there is an immediate upward flexure in the curve; a depressing agent, on the other hand, lessens the slope of the curve.
I shall now give a few typical examples of the employment of the Crescograph for investigations on growth: the first example I shall take is the demonstration of the influence of variation of temperature.
Stationary method: Experiment 52.—The records, given in [Fig. 59]a, were taken on a stationary plate. The specimen was S. Kysoor; the Crescographic magnification was two thousand times, and the successive dots at intervals of 5 seconds. The middle series, N, was at the temperature of the room. The next, C, was obtained with the temperature lowered by a few degrees. Finally H was taken when the plant-chamber was warmed. It will be seen how under cooling the spaces between successive dots have become shortened, showing the diminished rate of growth. Warming, on the other hand, caused a widening of intervals between successive dots, thus demonstrating an enhancement of the rate of growth.