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Fig. 114. — A tank for warm baths, 

 heated from below by a radiator, 

 r, and covered with felt, s {after 



Molisch) . 



and begin to bloom, while the controls, though receiving an identi- 

 cal treatment except being subjected to the action of ether, will 

 remain in full dormancy (Fig. 113). 



Exposure to a warm bath is still more simple. The aerial parts 

 of the plants are immersed in water at 30 to 35° C. and 9 to 12 hr. 

 (Fig. 114) after which the plants are transferred to a place favor- 

 able for growth. It is interesting 

 to note that the effect of warm 

 baths and of ether are purely local. 

 Accelerated development takes 

 place only in buds and branches 

 which have been exposed directly 

 to the stimulants. When a lilac 

 bush is placed in such position that 

 only part of its branches will be in 

 warm water, the others remaining 

 outside, then in a few days a sharp 

 difference between the development 

 of these branches will be observed 

 (Fig. 115). 



Besides the treatments with ether and warm baths, several 

 other methods to induce plants to break their rest period have been 

 recently discovered. Plants may be forced by various volatile 

 substances, such as prussic acid, thymol, camphor, acetone, ethyl- 

 ene, illuminating gas, tobacco, and other fumes. Cutting of the 

 buds, injection of water or salt solutions, exposure to various rays 

 and radium emanation, and many other external influences will 

 hasten the breaking of buds. So, too, a considerable acceleration 

 in development will be observed after freezing. Plants which have 

 remained during the winter in a warm room will start to grow later 

 than those subjected to the action of frost (Fig. 116). 



The mechanism of the effects of these stimulants is still un- 

 known. Some authors are of the opinion that they increase the 

 permeability of protoplasm and thereby induce growth. Others 

 hold that they increase the oxidation processes in the cells and thus 

 stimulate its vital activities. By studying the effects of ether 

 treatment at different times in the fall and winter, Johannsen came 

 to the conclusion that its influence is not the same at different 

 periods. This he considers an indication that the state of rest 

 likewise varies. He distinguishes three conditions of rest: a pre- 



