THE SEEDLING AND YOUNG PLANT. 41 



converse occurs the first spiral vessels arise near the 

 center of the stem, and development proceeds centrifu- 

 gally from the first. We may begin our study of the 

 shoot by tracing the course of the vascular bundles, 

 which, it must be remembered, are the channels of 

 communication between the water-supply at the roots 

 below and the leaves and young parts of the shoot 

 above. 



If we cut a transverse section of the terminal bud of 

 the oak, as close to the tip as possible, we shall obtain a 

 preparation of the young axis consisting entirely of em- 

 bryonic tissue, all the cells of which are practically alike 

 small, polygonal, thin-walled cells, with large nuclei 

 and much protoplasm, but without sap-vacuoles ; these 

 cells are in a state of active division, those in the in- 

 terior dividing successively in all planes. Those which 

 form the peripheral layer, however, are already distin- 

 guished by only dividing in the two planes at right 

 angles to the periphery, and they constitute the primi- 

 tive epidermis. There is no structure corresponding to 

 a root-cap. 



Transverse sections a little lower down show differ- 

 ences of the following nature : In the first place, the 

 outline of the section tends to be somewhat pentagonal, 

 the points of origin of the very young leaves being at 

 the angles of the pentagon in accordance with their 

 phyllotaxis i. e., the order in which the leaves are ar- 

 ranged on the stem. This is of such a nature that each 

 leaf stands some distance above and to one side of its 



