ROOT GROWTH AND TEMPERATURE 321 



root, but are present in all growth curves which cover a sufficient 

 length of time. 



The rate of growth in any individual growing in soil and 

 under constant conditions of soil and air temperature and of 

 illumination, may vary in one and the same experiment from 

 100% to about 300%. And the extreme range in rate variation 

 between different individuals growing under the same condi- 

 tions may be much gi-eater than this. 



The greatest variation in the rate of growth was observed 

 in roots which were 50 mm., or less in length. Although the 

 length of the root at the time of the ''grand period" of growth 

 was not especially studied, the ''grand period" appeared to 

 occur when the root was about 50 mm. in length. The behavior 

 of the root as regards the growth rate, therefore, and as regards 

 the variation of whatever kind in the rate, is probably to be 

 associated with the relation of the time of observation to the 

 root's development or more specifically to the "gi-and period" 

 of growth. 



METHODS 



The sahent featiu-es of the method followed in the experi- 

 ments, and in the procedure, may be briefly presented. Seed- 

 lings only were used. Quick germination was secured by fil- 

 ing a slot in the outer seed coats to admit water more readily. 

 x\fter lying a few hours in water the seeds were transferred to 

 glass tubes, 1.7 by 44 cm. in size, which contained sifted sand. 

 The soil was kept continuously moist by frequent watering with 

 tap water, or in some cases Knop's solution was substituted. 

 However, it was learned that for the short time the experiments 

 ran, the roots grew equally well in either the solution or the 

 tap water, so that for the most part water only was used. The 

 tubes were kept in a thermostat, arranged so that the shoots 

 projected from it, and the soil did not usually vary more than 

 0.5°C. during the course of any experiment. In some instances 

 the chamber in which the thermostats were situated was pro- 

 vided with a means of controlling the temperature independ- 

 ently of that of the thermostat. In others the shoots were ex- 



PHE PLANT WORLD, VOL. 20, NO. 10 



