286 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1919. 
in our latitude?’ It must be said in reply that there are. And it 
will be worth while to consider some of these causes, for not only are 
they of interest in themselves but also, instead of weakening the 
hypothesis here presented, they serve to strengthen and confirm it. 
The data may best be presented through a series of illustrations. 
The pruning of a long-dormant plant will often start it into 
growth. (See pl. 10.) 
Girdling produces a similar result. (See pl. 11, fig. 1.) 
Notching the stem does the same. (See pl. 11, fig. 2.) 
Rubbing the stem also starts the plant into growth. (See pls. 12 
and 13.) 
In all these examples of the stimulation of growth by injury it is 
conceived that the enzyme is brought into contact with the starch 
as a direct result of the breaking and straining of the cells. Sugar 
is then formed and growth begins. ~ 
It should be observed’ that when a normal chilled plant starts 
growing it grows from many buds (pl. 14), for the effect of the 
chilling on sugar formation is general. When a dormant plant starts 
growing as the result 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 chill- 
ing. 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 pls. 
15 and 16.) The new growth of the stem is confined to the one or two 
buds, just as was found to be the case with growth induced by 
injury. My interpretation of the phenomenon is that as death ap- 
proaches the cell membranes become weakened in much the same way 
as when chilled; the enzyme 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 
become dormant in the dry season and'start into growth again at the 
coming of the rainy season. ‘Tropical plants probably have various 
methods of coming out of their dormancy, and there is every reason 
