28 THE OAK. 



transverse section exactly at this place we should see 

 no differentiation into axial cylinder and root-cortex, 

 etc. ; the small circular mass would consist of cells 

 all alike, and with very thin walls and full of dense 

 protoplasm. 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 farther 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 x) ; 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-cyl- 

 inder is sharply marked and has well-developed vascular 

 bundles, 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 grow- 

 ing-point, and consisted of embryonic tissue with the 

 cells all alike. Or we may put it in a different way 

 thus : the present growing-point consists of embryonic 



