44 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Primrose, stand immediately in the front of the petals. In the Primrose 

 itself no trace of any such suppressed whorl of stamens is ever apparent. 

 In a large number of plants which are habitually — normally — without 

 a corolla, the stamens, as would be expected, stand in front of, and not 

 alternating with, the sepals. 



Although the organs of flowers are usually grouped in distinct whorls, 

 yet in many are they spirally arranged ; and when this is the case they 

 can be represented by some fraction of the series given for alternate 

 leaves.* 



A point now to be particularly observed is that these two arrange- 

 ments, viz. the "spiral" and the " verticillate " (or " whorled," including 

 the " opposite "), appear to be due to forces acting independently of each 

 other ; for it is rare to find whorls passing into spirals, and still rarer 

 for spirals to pass into whorls — if, indeed, it ever occurs. 



The Jerusalem Artichoke, however, furnishes many illustrations of 

 the former process, and in some instances of the latter, though no gradual 

 transition from a spiral to "verticillate" or opposite conditions ever 

 occurred in the cases examined. 



The following will enable it to be understood how a passage from 

 opposite or verticillate leaves into spiral arrangements can be effected : 

 The change from the opposite (decussate) leaves into the f divergence 

 occurred somewhat frequently as follows : A pair of leaves slightly con- 

 verge to one side, the angular distance between them being about 150°. 

 The succeeding pair likewise converge, but have a somewhat less angle, 

 one of the leaves in each case becoming slightly elevated by the develop- 

 ment of an internode ; so that the sixth leaf now appears over the first, 

 or the lowest leaf of the first pair that converged to one side. It must 

 be noted that the angles between the radii drawn to the position of the 

 converging leaves do not accurately contain 144°, or § x 360°. But as 

 the spiral arrangement is continued up the stem and into the terminal 

 bud, the leaves seem to " right " themselves, as it were ; so that the 

 appearance of the spiral in the neighbourhood of the summit is more 

 accurate than at the point of departure from the highest pair of opposite 

 leaves. 



The change from opposite and decussate leaves to the 5th arrange- 

 ment will be seen by the following diagram. The leaves are represented 

 as still standing in their original positions ; but in becoming alternate 

 one leaf of each pair stands at a higher level than that of its companion. 

 Now the order in which the leaves are raised above their fellows is seen 

 by the numbers, lying on a long spiral line (fig. 3). 



The passage from opposite and decussate positions to the \ arrange- 

 ment is effected by three processes. First, the second pair of leaves is not 

 quite at right angles to the first chosen. Similarly the third pair is not 

 at right angles to the second ; a slight twist, as it were, has been given to 

 both in the same direction. Secondly, the order of uplifting of one leaf 

 of each pair to a higher level than that of its companion is in a definite 

 and constant order, as shown in fig. 3. This causes a short internode to 



* A point worthy of note is, that the free portions of the corolla of a primrose 

 overlap one another in just such a way as corresponds to the \ arrangement of spiral 

 loaves ; though, of course, they are now actuully verticillate. 



