Grossenbacher — Radial Growth in Trees. 3 



habit of such plants. 3 He maintains that the periodic or discon- 

 tinuous habit of vegetative activity in plants is due to an alter- 

 nation of favorable and unfavorable seasons of the year or to a 

 periodicity of the climate, and that it, therefore, may be made 

 continuous by modifying the environment. From his experi- 

 mental work he concludes that dormancy is due to a reduction in 

 one or more of the factors essential for growth, such as tempera- 

 ture, moisture and mineral nutrients, below the required amount ; 

 and that when such conditions occur the further manufacture 

 and accumulation of organic foods inhibits the action of the 

 enzymes necessary for growth. A timely increase in the limit- 

 ing factor is said to either prevent or terminate a period of 

 dormancy in most cases. The reduction in the supply of mineral 

 foods was found to be a very important factor in inducing dor- 

 mancy and, therefore, raising the temperature and increasing the 

 supply of water and mineral foods was often found to force 

 plants into growth. Berthold 4 also concluded that a reduction 

 in the supply of nutrient salts is the chief factor inducing a ces- 

 sation of terminal growth. This same conclusion was more re- 

 cently drawn by Lakon 5 who caused the buds of various decidu- 

 ous trees and shrubs to open when cuttings were placed in 

 Knop's solution. Klebs thinks that in many cases the individ- 

 ual periodicity of the different branches and twigs of a tropical 

 plant are due to differences in transpiration and mineral nutrient 

 supply of such structures. It is thought probable that there 

 may be a periodicity in the supply of mineral nutrients in the 

 tropics which at times becomes a limiting factor inducing par- 

 tial dormancy. On the other hand Smith 6 maintained that 

 elongation growth of various Ceylon plants is controlled chiefly 

 by the temperature and water supply; sometimes one and then 

 the other or perhaps both acting together as the limiting factors. 

 In his interesting study of the second growth occurring on 



5 Klebs, G. tiber die Rhythmik in der Entwickhing der Pflanzen. 



Sitzungsber. Heidelber. Akad. Wiss. Math. Naturw. Klass. 23. 1911. 

 pp. 84. 



* Berthold, G. D. W. Untersuchungen zur Physiologie der pflanzli- 

 chen Organization. 2:131-257. 1904. 



B Lakon, G. Die Beeinflussung der Winterruhe der Holzgewachse 

 durch die Nahrsalze. > Ein neues Frfihtreibenverfahren. Zeit. Bot. 

 4:561-82. 1912. 



' Smith, A. M. On the application of the theory of the limiting factors 

 to measurements and observations of growth in Ceylon. Ann. Roy. Bot. 

 Gard. Peradeniya. 3:303-75. 1906. 



