;:> 1 REV. G. HENSLOW ON THE VARIATIONS IN 



>rd 1< f is isolated ; but the 2nd, though still confluent with the 1st (as indicated by 

 the thickened line in the fig.), is slightly raised. Similarly the 5th, though united to 

 the 4th by the broad base of the petiole, is at a slightly higher level. The same remark 

 ;i|)|)lies to the 8th ; but the internode between the two confluent leaves, the 7th and 8th 



i now much increased. Above the 8th the leaves are entirely free; and finally the 9th 

 vertically over the 1st, so that the f divergence is established. 



i 



IY r . Transitions from the Tricussate arrangement into Spirals of the Secondary 

 i. No direct change from tricussate into \ or i occurred. 



Q ~ ^*.... V x*vs U „t»* uu mvy, o yj L . 



ii. A change from verticils of threes into the f was frequent. It takes place in the 



following manner:— The 1st step is to cause the three leaves of the different whorls to 



iparate -lightly by a development of their internodes. Then, if any two consecutive 



be examined, the order of succession of the six leaves (No. 1 being tbe lowest leaf) 



thus 



6 



3 7 9 2 



4 8 5 



1 



in which it * ill be noticed that the 4th leaf, instead of being over the interval between 

 the 1st tnd 2nd, is over that between the 1st and 3rd; so that the angle between the 1st 

 and 2nd leaves, or between the 2nd and 3rd, is double that between the 3rd and 4th. 



These latter, it will be remembered, are separated by a long internode. The same order 



'.tarns with the succeeding whorls; the nodes, however, are now much more widely 

 parated, while a true spiral arrangement, with the same angular distance between 







its leaves, is ultimately secured, and is henceforth continued uninterruptedly into the 

 terminal bud, and represented by the fraction f . 



Another method of separation of the three leaves of the whorls consists in one leaf 

 only becoming isolated (as was the ease in the transition from tricussate into f diver- 



gence), wh.le the other two remain coherent at the same level. The result obtained in 



this case, rt will he remembered, is identical with that secured in certain cases of change 

 from deeu ,u leaves, where a third leaf is thrown out at right angles to the diameter 

 ,.asang throe h the supposed original positions of the opposite leaves, which now 



-« 



to one side 



From this stage either of the two following results may 



'!:;„; :;; rzS 't the ,f imate s<Tan,,ion ° f the tw ° ™^ ] — ., 4 ** «. 



Z on ; ,r 1 T 56 ° f thC PaSSa " 6 fr ° m d — te ^ves nto that diver- 



c ;' h ^ of ££*££ :: i u r t leaves may never separate at au> so 



iii Although fl,n 1 . ! 6 Smgle leaf occurs up the stem to its summit. 



u, Although the T arrangement is by far the most general of the secondary scries, as 



arising from tl 



aeeuracv. The dS h£L t™^™ ° COasionaI1 y -cur with more or less 



l«rf. in' 1..^. .,' " 1 °-, 8) lUustrates a case « ^vhieh A commenced with the 18th 



leaf, in having the 21th almost 



- u fc ^ „ mm. m*. mi Braun , 8 work on . rhylIotasi3( „ by ^ — Md 



