326 PLANT PHYSIOLOGY 



lie dormant during the " winter" months. Other trees have be- 

 come evergreen in their new environment and have lost the char- 

 acteristics of their native region very quickly. The peach becomes 

 nearly evergreen the first generation and completely so in the 

 second in Ceylon, where it bears flowers and fruit throughout the 

 year like the oranges in California. 



With some plants the periodicity seems to be a question of 

 internal factors and with others it is purely a question of the en- 

 vironment. In the temperate climate, it is a familiar sight to see 

 peach or other fruit trees blooming in the fall if the summer has 

 been a favorable one for food manufacture and when dry weather 

 in the late summer is followed by abundant, warm showers. 



Seeds also show a similar resting period. Planted immediately 

 after " ripening" they often fail to grow, but must remain in a 

 dormant condition for some months (Chap. XXXI). 



The forcing of buds, bulbs, and other resting organs is a prob- 

 lem whose solution means much to the horticulturist and florist. 

 Aside from providing favorable temperature conditions, much 

 experimentation has been carried on of late with anaesthetics 

 like chloroform, ether, etc. The plants are first exposed to ether 

 vapor for 24-48 hours and then placed under favorable growth 

 conditions. In this way lilacs have been made to bloom in three 

 weeks which otherwise would require double that period. Bulbs 

 and gladiolus corms have been hastened two to three weeks 

 by placing in an atmosphere containing a teaspoonful of ether for 

 every 100 c. c. of air space; and Howard (1910), experimenting 

 with a great variety of trees and shrubs, found that the ether 

 treatment shortened the time required for the opening of the 

 buds about a week or ten days. The effect of the ether is not 

 exactly known, but it probably increases the permeability of the 

 cells, with the result that the food is more readily available. 



Hot water has also been used as a method of forcing. The twigs, 

 bulbs, or roots are placed in water at a temperature of 30-35° C. 

 for about ten hours. The effect is similar to that produced by 

 the ether treatment and, because of the practical advantages in 

 application, this method of forcing is to be recommended for 

 ordinary work. Coville, on the other hand, has emphasized the 

 use of cold treatment in forcing. He believes that the change 

 from starch to sugar associated with chilling and low temperatures 

 acts as a stimulus and may thus start precocious development. 



