Grossenhacher—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 7 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 
Enop’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 
* Klebs, G. liber die Rhythmik in der Entwieklung der Pflanzen. 
Sitzungsber. Heidelber. Akad. Wiss. Math. Naturw. Klass. 23. 1911. 
pp. 84. 
4 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 Fruhtreibenverfahren. Zeit. Bot. 
4:561-82. 1912. 
6 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. 
