58 CARNEGIE INSTITUTION OF WASHINGTON. 



Some individuals were followed without interruption for periods of 

 70 days under measured or controlled conditions. 



The reduction and anaU'sis of the data concerning growth in plants 

 has made it possible to formulate some advanced general statements. 

 The whole process of enlargement includes the synthesis, or solution 

 of food material by hydrolysis of accumulated supplies, the conduction 

 of solutions to the enlarging tracts and its conversion into the special- 

 ized formative material necessary for the growth of organs of all kinds. 

 This is followed by the incorporation of the material in the plasmatic 

 colloids and their derivative and accessory structures. 



Photosynthesis (or other reduction processes), hydrolysis, and the 

 final utilization of food-material in the construction of formative 

 substances are chemical processes the velocity of which is so influenced 

 by temperature as to be increased 2 to 7 times for every rise of 10° C. 

 The delicate response of growth by changes in rate under variations of 

 1° to 2° C. support the inference that temperature is the dominant factor 

 in controlling growth by its effect on the availability of the food-supply. 

 This agency, of course, also affects the rate of conduction of food- 

 material and of its introduction into growing masses, but in ver}^ much 

 less degree than it exerts on chemical reaction. 



The utilization of food-material, in which the carbohydrates are the 

 most important constituent, includes some breaking down of the sugars, 

 the initial changes being enzymoticallj'^ induced, followed by oxidation 

 of the waste or derivatives (organic acids) not actually used as building 

 material. The rate at which the first stage of the process proceeds 

 depends upon the removal of the acids, which not only check respira- 

 tion, but also by their effect on the plasmatic colloids lessen the hydra- 

 tation capacity or swelling power of plasma and cell-walls. The acid 

 wastes are disintegrated by the action of light, with a resultant acceler- 

 ation of respiration and of the construction of ''formative material." 

 The capacity of the growing parts to take up water is increased coinci- 

 dently. 



The above effects are well exemplified by the behavior of growing 

 joints of opuntia, of which several hundred records are available. The 

 daily history of a growing joint includes an acceleration in the forenoon, 

 during which time the acid wastes are being broken down by Ught, the 

 maximum rate of growth being reached after noon with the consump- 

 tion of the accumulated food-material. The elongation slackens or 

 proceeds according to the diminished supply, and with the coming of 

 darkness may actually cease by the hemming action of accumulated 

 acids. Actual shortening may ensue during the night because of 

 decreased hydratation capacity resulting from low temperature and 

 acidulation. The dawn brings the disintegrating effect of light on 

 acids and the resumption of growth. 



