RADIAL STRUCTURE. 



487 



shoot-axis is situated, to the points marked i, 2, 3, 4, 5, in the midribs of the leaves, 

 and produced to the other sides, five divisions of the entire system are obtained, in 

 which the transverse sections of the subsequent leaves 6, 7, 8, 9, 10 are also arranged; 

 only care must be taken lest error be made on account of a few minor irregularities, 

 which depend in part upon the mutual pressure of the organs closely packed together 

 in the bud-scales I-V, but which are in part artificially produced in the cutting. It is 

 noticed further that the leaves numbered 1-9 in order of age, in spite of the radial 

 arrangement, are nevertheless not arranged in circles as in the preceding examples ; on 

 the contrary, an inspection of the same shoot after its unfolding, when the interfoliar 

 parts have elongated, would demonstrate that the leaf 2 is situated higher than i, 3 higher 

 than 2, and so forth. The leaves are, as is usually said, arranged spirally around the 



W'P'^^^W //Vi 





Fig. 323.— Transverse section through a winK 

 scales ; 1—9 the pinnate leaves, with 



■ bud of Spiraa sorbi/oUa. I—iy bud- 

 heir stipules {numbered similarly). 



axis, that is, if a line is supposed to run round the shoot-axis so that it takes in the 

 points I, 2, 3-9, it forms a spiral. By means of longitudinal sections such a shoot 

 with spirally arranged out-growths would never be divided into actual or even ap- 

 proximately symmetrical halves, as the young flower considered above; nevertheless 

 it is advantageous on physiological grounds to regard this very common case also as 

 belonging to the radial type. The off-shoots radiate in five directions, not from the 

 same but from different levels on the shoot-axis, a fact which is of subordinate 

 importance for physiological conclusions. Instead of a transverse section then a 

 so-called diagram serves to represent the arrangement not only on an individual 

 shoot but even on an entire shoot-system. The whole is supposed to be looked at 

 from above, and a sufiicient number of concentric circles are drawn on the paper ; 



