INTRODUCTION 



13 



angled stem. If we hold it so that the youngest leaf 

 (1) of the piece of shoot figured sits on the uppermost 

 ridge in Fig. 5, the leaf immediately above (2) rises not 

 from the next ridge, but the next but one, that on the 

 lower left-hand side. The next (3) sits on the ridge 

 on the upper right-hand side. No. 4 is on the left. 

 Finally, leaf No. 5 is on the ridge forming the lower 

 right-hand edge of the stem. I say finally, because this 

 completes the series. Leaf No. 6 is on the same ridge 



Fig. 5. — Whorl of Bramble leaves. 



as, and corresponds to No. 1, leaf No. 1 to leaf No. 2, 

 No. 8 to No. 3, and so on. 



The leaves, in fact, are not on the ridge next to 

 the ones immediately above and below, but on the next 

 but one. Thus, then, each whorl consists of five 

 leaves arranged in a double spiral round the stem. 

 This is known as the 2/5 arrangement. Incidentally it 

 throws light on the pentagonal form, of the stem. The 

 arrangement is, however, not quite so obvious as would 

 otherwise be the case — firstly, because the stem is often 

 somewhat twisted, and, secondly, because the petiole of 

 the leaf is itself sometimes bent, so that the leaf may 



