28 THE OAK 
and other peculiarities ; and if we could take a trans- 
verse section exactly at this place we should see no 
differentiation into axial cylinder and root-cortex, &Xc. 
—the small circular mass would consist of cells all 
alike, and with very thin walls and full of dense proto- 
plasm. This undifferentiated formative tissue is called 
the embryonic tissue of the root (fig. 6, m). A little 
behind this we see the axis-cylinder and root-cortex 
already formed ; still further away we see the vascular 
bundles appearing, first as very thin cords, and then 
getting stronger and stronger as we recede from the tip 
(fig. 6, ph and «); and similarly we trace the gradual 
development of the other parts in acropetal succession— 
i.e. the nearer we go to the apex the younger the parts 
are. 
Now, there is a conclusion of some importance to be 
drawn from the putting together of these facts—namely, 
that all the structures found between the embryonic 
tissue at the tip of the root and the place where the root 
joins the stem have been gradually formed from the 
embryonic tissue in acropetal succession. We may 
picture this by marking a given level on the root, 
some distance away from the tip, where the axis-cylinder 
is sharply marked and has well developed vascular bun- 
dles, the root-cortex is distinct, and the piliferous layer 
bears root-hairs, and remembering that so many days or 
weeks ago this very spot was in the then growing-point, 
and consisted of embryonic tissue with the cells all alike. 
Or we may put it ina different way thus: the present 
