158 



Dr. H. Airy on the 



[June 15 J 



its influence nevertheless appears to depend on the solar activity (a result 

 similar to that obtained by Mr. J. A. Broun in the case o£ terrestrial 

 magnetism), it is argued that even if there be a connexion between mean 

 annual temperature-range and the sun-spot period, yet we cannot expect 

 both periods to march together in the same way, inasmuch as the first is 

 due entirely to the sun, while the latter appears to depend upon the 

 moon as well. 



This may possibly explain the redundant temperature fluctuation already 

 alluded to ; but the discussion of the subject must be further advanced 

 before w^e can pronounce upon this point. 



XVI. " On the Leaf- arrangement of the Cro wherry {Empetrim 

 nigrum). By Hubert Airy^ M.A., M.D. Commnnicated by 

 Charles Darwin, M.A., F.B.S. Received M^y 8, 1876. 

 (Abstract.) 



Pursuing the study of leaf -arrangement, the author finds that the 

 crowberry of our moors (Empetnim nigrum) habitually exhibits a peculiar 

 mo le of variation in the arrangement of the leaves on different parts of 

 the same twig. Out of fifty crowberry-twigs taken at random, only four 

 (and these fragments) preserved the same arrangement throughout. In 

 the remaining forty-six the leaf -arrangement was found to undergo a pro- 

 gTessive change in ascending from the base of the twig to the summit — 

 a change from a simpler order to others more complex. In general the 

 basal order was that denoted by the fraction | ; and this was found to pass 

 most frequently into |-, which in turn was found to pass into |, with or 

 without an intermediate set of whorls of 4 : |- generally passed into 

 whorls of 5, sometimes into y^y, which was the most complex arrange- 

 ment that was met with in this plant. The following is a hst of the 

 transitions found in the fifty specimens : — 



Transition from |- (or -|) to |- occurred 22 times. 





do. do. 



?j 



2 

 y 



JJ 



5 



JJ 



5? 



„ do. do. 



5J 



whorls of 5 



JJ 



1 



JJ 



5? 



,, whorls of 3 



J? 



2 



7 



JJ 



2 



JJ 



5» 



2 



" 7 



JJ 



whorls of 4 



JJ 



10 



JJ 



J) 



2 



" 7" 



JJ 



a* 



JJ 



2 



JJ 





2 





2 





9 





5J 



" 7 



JJ 



"9 



JJ 





JJ 



5' 



,, whorls of 4 



JJ 



2 



9" 



J) 



5 



JJ 



5? 



„ a* 



JJ 



2 



1 1 



JJ 



1 



JJ 



?5 



f 



JJ 



whorls of 5 



JJ 



5 



JJ 



>) 



" "9 



JJ 



2 

 TT 



JJ 



1 



JJ 



JJ 



„ whorls of 5 



JJ 



_2_ 



1 1 



JJ 



1 



JJ 











Total 



64 





* By a the author denotes a 4-, 6-, 10-ranked order, such as is found in heads of 

 Dipsacaceie. 



