THEIR ARRANGEMENT. 



147 



ondary spirals nearest the vertical rank in each direction, when 

 there are more than two, as there are in all the succeeding cases. 

 245. A similar diagram of the f arrangement introduces a third 

 set of secondary spirals, in addition to the two foregoing, ascending 

 in a nearer approach to a vertical line, and with a higher common 

 difference, viz. 5. There are accordingly five of this sort, viz. 

 those indicated in the diagram by the series 1, 6, 11, 16; 4, 9, 

 14, 19, 24 ; 2, 7, 12, 17, 22 ; 5, 10, 15, 20, 25 ; and 3, 8, 13, 18, 

 23. The highest obvious, spiral in the opposite direction, viz. that 



Vertical Projection 

 of the | Arrange- 

 ment. 



25 



24 



21 



19 



18 



17 



16 



15 



14 



13 



12 



n 



10 



Vertical Projection of the A 



Arrangement. 



27 



26 



25 



24 



23 



22 



21 



20 



19 



13 



17 



16 



15 



14 



13 



12 



11 



10 



of which the series 1, 4, 7, 10, 13 is a specimen, has the common 



FIG. 176. A cone of the White Pine, on which the numbers are laid down, and the leading 

 higher secondary spirals are indicated : those with the common difference 8 are marked by dotted 

 lines ascending to the right; two of the five that wind in the opposite direction are also marked 

 with dotted lines : the set with the common difference 3, in one direction, and that with the 

 common difference 2, in the other, are very manifest on the cone. 



