THE NATURE OF THE GROWTH RATE.* 



By H. S. reed. 



{From the University of California Graduate School of Tropical Agriculture and 

 Citrus Experiment Station, Riverside.) 



(Received for publication, March 5, 1920.) 



Recent studies (Robertson (1908) and Reed and Holland) have 

 shown that the rate of growth of certain organisms corresponds to the 

 rate of an autocatalytic reaction. At the present time it seems profit- 

 able to extend the inquiry to several different types of plants and to 

 learn something of their growth rates. 



The Growth Rate of Pear Shoots. 



During the season of 1919, weekly measurements were made of the 

 growth of shoots of young Bartlett pear trees. The young shoots of 

 the pear (Pyrus communis L.) are good material for such inquiry be- 

 cause of their vigorous growth and generally unbranched condition 

 during the 1st year. The trees on which the shoots were selected 

 and marked had been planted 3 years previously. They made good 

 growth during the season in which the measurements were being made, 

 but, on account of their age, produced no fruit. On April 24, 1919, 

 fifty shoots on twenty-six trees in different parts of the orchard were 

 selected. One shoot was subsequently broken and had to be elimi- 

 nated. The remaining forty-nine shoots were measured each week 

 until September 3, at which time elongation had ceased. The length 

 of each new shoot was determined weekly by measuring the distance 

 from its base to the apical bud. Though a few shoots did not cease 

 elongation until the 133rd day (September 3) the average length of 

 the growing season of all shoots was 97 ±1.7 days. 



* Contribution No. 65 from the University of California Graduate School of 

 Tropical Agriculture and Citrus Experiment Station. 



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