THE SEEDLING AND YOUNG PLANT 41 
petal order from these points. In the young stem the 
exact converse occurs—the first spiral vessels arise near 
the centre of the stem, and development proceeds cen- 
trifugally 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 com- 
munication 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 
embryonic 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 
interior 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 dif- 
ferences 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—7.e. the order in which the leaves are 
arranged on the stem. ‘This is of such a nature that 
each leaf stands some distance above and to one side of 
