90 



STRUCTURAL BOTANY. 



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

 fore, be ^ ; 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, tli3 

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

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

 pressed by -j 5 ^. 



299, Phyllotaxy of the cone (cycle 8 /2i> of Finns serotina. The scales nre 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. 300. 

 Cherry cycle (3/ 5 ) as viewed from above, forming necessarily that kind of aestivation called quincunciaL 



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

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

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

 of Pine figured above ( 299). 



Review. 2(51. What is the etymology of the word phyllotaxy ? 292. Explain '' Lvs. 

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

 Scattered ? Fasciculate ? Verticillate ? Reduce to two general type?. 2H3. What ex- 

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

 20-1. Carefully explain the Elm Cycle. Why is its index J ? 263. Explain also tht Aldei 

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

 plain flgs. 299, 300. 



