90 



STRUCTURAL BOTANY. 



sum of the two preceding. The fifth terms in order will, there- 

 fore, be -f$ ; and this arrangement is actually realized in 



269. The White Pine cycle. In the young shoots of the 

 White Pine, in cones of most Pines, in Flea-bane (Erigeron 

 Canadense), etc., the fourteenth leaf stands over the first, th3 

 fifteenth over the second, etc. The spiral thread makes five 

 revolutions to complete the cycle, which is, therefore, truly ex- 

 pressed by -f-%. 



299 



299, Phyllotaxy of the cone (cycle 8 /2i^ of Finns serotina. The scales are numbered (1, 2, 3, etc.) in 

 order as they occur in the formative cycle. Between 1 and 22 are 8 turns and 21 scales, etc. 330, 

 Cherry cycle ( 2 / 6 ) as viewed from above, forming necessarily that kind of aestivation called quincuncial. 



270. The Houseleek cycle is next in order, expressed by 

 the fraction (^y 3 ) -^j, having eight turns and twenty-one leaves. 

 Examples are found in the Scotch Pine, Houseleek, and the cone 

 of Pine figured above ( 299). 



Review. 261. What is the etymology of the word phyllotaxy ? 262. Explain " Lvs. 

 radical" Lvs. canline Lvs. ramial. What is the alternate arrangement? Opposite? 

 Scattered 'Fasciculate ? Verticillate ? Reduce to two general types. 263. Wlkit ex- 

 periment reveals the true nature of these types? State the Law of plant-development. 

 264. Carefully explain the Elm Cycle. Why is its index i ? 265. Explain also th*. Aldei 

 Cycle and its index and the other cycles. 268. Show the relation of these cycles Ex- 

 plain figs. 299, 300. 



