42 THE OAK. 



next neighbor below, and if a line be drawn from the 

 insertion of any one leaf through the points of inser- 

 tion of those above, it will describe a spiral, and will 

 eventually come to a leaf standing directly above the leaf 

 started from. In doing this the spiral line will pass twice 

 round the stem, and through the points of insertion of 

 five leaves. This is shortly expressed by two fifths. 



The preyiously homogeneous embryonic tissue in 

 the section now shows certain patches of grayer, closer 

 tissue, arranged round the center in a peculiar manner ; 

 these are transverse sections of the young vascular 

 bundles strands which at present are distinguished 

 chiefly by the small diameter of their cells, whence the 

 darker gray appearance. 



These strands when young are called procambium 

 strands. Their cells are distinguished from the other 

 embryonic cells around by growing more in length and 

 dividing less frequently across their length, and by 

 growing less in breadth and dividing more often by 

 longitudinal walls. 



On transverse sections a little lower down there may 

 be seen a number of elongated and curved patches of 

 procambium, as shown in Fig. 9. On the section it will 

 be noticed that the larger strands are so arranged that 

 they inclose a five-angled mass of central tissue (the 

 pith), the five corners pointing to the angles of the 

 young stem to which the leaves are attached. At the 

 corners or ends of the rays just referred to are in some 

 cases two or three smaller strands. 



