1 56 Journal of Agricultural Research vol. xx, No. 2 



of injury, however, it usually starts, as shown in several illustrations 

 already presented, from a single bud, the one nearest the point of injury- 

 The injury is local, and both the sugar formation and the growth that 

 follows it are local. 



We are now brought to the consideration of a phenomenon which I 

 take to be of special significance — namely, the procedure by which the 

 dormant plant starts itself into growth in the absence of chilling. After 

 a blueberry plant has remained dormant at a warm temperature for a 

 very long period, sometimes a whole year, the tips of the naked branches 

 begin to lose their vitality. Just before or just after the death of the tip 

 a single bud, or sometimes two buds, situated next below the dead or 

 dying part starts growing (see PI. 27, B; 31, A). The new growth of the 

 stem is confined to the one or two buds, just as it was in the case of 

 growth induced by injury. My interpretation of the phenomenon is 

 that, as death approaches, the cell membranes become weakened in 

 much the same way as when chilled, the enzym passes through into the 

 starch storage cells, sugar is formed, and the adjacent bud begins to 

 grow. The process going forward here in a restricted portion of the 

 stem, and due to a local cause, is essentially the same as that taking place 

 generally over the plant, from a general cause, when the plant is chilled. 



In the Tropics some plants are able to grow continuously; others be- 

 come dormant in the dry season and start into growth again at the com- 

 ing of the rainy season. Tropical plants probably have various methods 

 of coming out of their dormancy, and there is every reason to expect 

 that some of them will be found to accomplish this act in the same way 

 as our long dormant greenhouse plants, by the weakening of their cell 

 membranes. This, I have endeavored to show, is in its effect substan- 

 tially identical with chilling. 



6. The twigs of trees and shrubs after their winter chill- 

 ing AND THE TRANSFORMATION OF THEIR STARCH INTO SUGAR MAY BE 

 REGARDED AS MECHANISMS FOR THE DEVELOPMENT OF HIGH OSMOTIC 

 PRESSURES WHICH START THE PLANT INTO GROWTH. 



Food in the form of starch can not be utilized by a plant directly. 

 The starch must be changed into sugar before it can be used in making 

 new growth. But this transformation does more than make the starch 

 available as food for the growing plant. It serves also to increase the 

 tendency of the cells to swell and enlarge. In the form of starch the 

 material is inert in the creation of osmotic pressures, but when trans- 

 formed into sugar it becomes exceedingly active. According to the rigid 

 experimental tests of H. N. Morse and his associates, a normal solution 

 of cane sugar at 32 F. has an osmotic power of 25 atmospheres of pres- 

 sure. It has been demonstrated that there sometimes occur in the cells 

 of plants osmotic pressures as high as 30 atmospheres, or 450 pounds to 

 the square inch, a pressure sufficient to blow the cylinder head off an 



