Of cones and hemispheres

Here is a visualization of the annual superimposition of cones which represents tree growth (lowest/earliest cones are not shown). We can extend this a little further. At the apex of each cone are laid down the buds which will grow into our new twigs next year. These grow in the same manner, expanding into the branches which subtend our expanding canopy (shown here as successive approximately-hemispherical helmets). The relationships which govern our tree’s physical development (which make a black walnut look like a black walnut, or a Norfolk Island Pine like a Norfolk Island Pine) are under close genetic control, and it is basically the annual variability in the environment which results in our tree in any given year growing a little bit more or a little bit less.