Development of Mechanical Tissue . 517 
The first point can best be studied by a comparison of one- 
year-old fruit-bearing shoots and one-year-old vegetative 
shoots, while a study of the second point requires that such 
shoots shall be chosen as promise to become permanent parts 
of the tree. Shoots fulfilling these conditions are found at 
the ends of the branches. Much of the fruit on both the 
Apple and the Pear is borne on short lateral shoots, which 
persist for a term of years, but which never become a part of 
the body of the tree. These shoots are known as‘ fruit-stubs.’ 
Their structure and its relation to the question under con- 
sideration will not be discussed in this paper. 
By a one-year-old fruit-bearing shoot is meant that part of 
the terminal growth made during the season of collecting, 
and which lies between the scars left by the preceding winter’s 
bud-scales at one end, and the bases of the fruit-stalks at the 
other. When collected in the fall, these shoots have com- 
pleted one year of growth from their formation in the buds 
the previous year. The vegetative shoots selected occupied 
the same relative position, and were of the same age as the 
fruit-bearing shoots. 
When growth begins in spring, the axis of the flower- 
bud lengthens rapidly, and bears at its apex a cluster of 
blossoms. Its complete growth in length is soon reached, 
and its continued vegetative existence is assured by the 
production of one or more lateral buds, which may or may not 
grow out into shoots during the same season. The fruit-bearing 
shoots average about 1*5 cm. in length, and are always more 
or less swollen. The swelling begins at the basal zone of 
scars, and is greatest at the apex of the shoot, just below the 
scar left by the breaking away of the fruit-stalk. By this 
scar, as well as by the swelling, a portion of a branch that has 
borne fruit during its first year may be recognized even until 
twelve years old. The age of such a part may be readily 
determined by counting the zones of bud-scars left at the base 
of each year’s growth. 
The shoots, both fruit-bearing and vegetative, were studied 
from cross-sections made serially from the basal zone of scars. 
