. Hydration and growth. Growth (Plants); Plants. 136 Hydraiion and Growth. of mm. daily at 16° to 18° C. showed a rate of 11 to 17 mm. daUy at 30° to 32° C. The rate of growth would be one which would be accepted as being in general conformity with the van't Hoff formula of chemical reaction, while as a matter of fact it is not widely different from the capacity for imbibition under the influence of equivalent tempera- tures. Experimental tests have already been described in which the upper limits of growth and the behavior of etiolated and green stems of Opuntia between 46° and ° C. a
. Hydration and growth. Growth (Plants); Plants. 136 Hydraiion and Growth. of mm. daily at 16° to 18° C. showed a rate of 11 to 17 mm. daUy at 30° to 32° C. The rate of growth would be one which would be accepted as being in general conformity with the van't Hoff formula of chemical reaction, while as a matter of fact it is not widely different from the capacity for imbibition under the influence of equivalent tempera- tures. Experimental tests have already been described in which the upper limits of growth and the behavior of etiolated and green stems of Opuntia between 46° and ° C. are not widely different. (Fig. 24.)^ The rapid and wide variations at these high critical temperatures are to be contrasted with the steady rate of a growing green joint main- tained at 30° C. for 38 hours. The illumination in the daylight period apparently did not affect the rate of mm. per hour. 12 12 m 12 12 m. ) Fig. 25.—Tracing of auxograpMc record of variations in thickness of joint of Opuntia approach- ing maturity. Upward movement of pen denotes increase in thickness, X45. Measurements made from place between areoles near base of joint. Scale ruled to 5 mm. and 12-houT intervals. It is to be noted that the hour is set forward on the summer schedule. In addition to the great number of records of the variation of joints of Opuntia as to length, a few days' measurements of the thickness of a maturing joint were made in April 1918 in order to ascertain whether or not increases and shrinkages took place in all dimensions at the same time. The auxographic tracing in figure 25 gives the daily variation in thickness near the base of a maturing joint, which are seen to be correspondent to those in length. It is to be noted that the instrimient was necessarily adjusted so that increase was denoted by the upward movement of the pen, in a manner opposite to that in nearly all the other records. Later the bearing-lever of the instru- ment was
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectplants, bookyear1920
