GENERAL CHARACTERISTICS OF GROWTH 327 



When one part of a dormant blueberry bush was chilled and the 

 other part kept warm, the chilled portion had leaves and flowers 

 while the other portion was still dormant. It is also his opinion 

 that the forcing effect is associated with an increased permeability 

 of the cells to nutrient materials and to enzymes. 



At the Boyce-Thompson Institute these practical phases of 

 physiology are receiving much study, and Denny (1926) has 

 shown that potato tubers can be forced best by ethylene chlorhy- 

 drin, of the 224 chemicals tested. Tubers treated with the vapors 

 of this compound produced vines two feet high with young tubers 

 1 cm. in diameter before the untreated plants appeared above the 

 ground! Shrubs (lilac, Deutzia, and Azalea) and trees (Prunus 

 and crabapple) treated with the vapors of this compound or of 

 ethylene dichloride for 24-48 hours were in blossom 2-8 weeks 

 ahead of controls. It was also possible to force one bud and let 

 the opposite one lie dormant, showing that dormancy is a purely 

 local issue and is not related to the general reserves and conducting 

 tissue of the adjacent stems. 



Similarly, ethylene in very low concentrations (1 part in 4,000- 

 10,000) has been used to ripen oranges, bananas, lemons, and 

 tomatoes. Most of these fruits are nearly ripe internally, so that 

 the chief effect (but not all) seems to be connected with the de- 

 velopment of the pigment characteristic of the ripe fruit. Since 

 ethylene is used also in bleaching celery, evidently its principal 

 action here is to aid the breakdown of chlorophyll preparatory to 

 the formation of the yellow or red pigment of the "ripe" fruit. 

 This " ripening" process may take only a few hours and thus 

 shorten by days the natural processes. 



Other methods used (with less success) to hasten plant develop- 

 ment and growth are the injection of K, Mn, Mg, and Fe salts 

 (Popoff); artificial light (Niethammer) ; and wounding (in the 

 case of bulbs) . This last method is thought to hasten the increase 

 of water, but all the substances used in forcing, as mentioned above, 

 probably increase the permeability of the cells and may also favor 

 enzymatic changes. These, however, like most vague suggestions, 

 are only another way of saying that we really know practically 

 nothing about the actual modus operandi. 



