632 REV. G. HENSLOW ON THE VARIATIONS IN 



other; bill above them the leaves gradually assumed some spiral form by shifting to th 

 lit or I I'i (*. e. of the observer in front), 

 i. X 





o instance 1 of a direct change from opposite leaves into the -^ arrangement presented 

 itself; indeed, to accomplish this, the divergence would have had to pass from one limit 



to the other, >. e. from 180° to 120 



u. The change from the decussate into the f divergence occurred not unfrequently. 

 The method by which it was eiFected will be understood by reference to the diagram 



(fig. 2), in which it will be observed that the positions of the leaves numbered 1 and 2 



are not irictly opposite, and that radii drawn from them to the centre do not pass at 

 'ght angles to the diameter through the asterisks which indicate the position of the 

 ;hest pair of opposite leaves; so that these radii include an angle of about 150° 



n 



Lgain, by a similar approximation of the 3rd and 4th, and of the 5th and 6th leaves, 

 we find, on completing the second turn of the spiral, that the 6th leaf is over the first; 



SO that a transition into the f divergence has been established from this point. 



It must be noted that the angles between the radii drawn from the centre through 



successive leaves of this first, and of what might be called transitional cycle, do n*ot 



lecnrately equal 144° or 1x360°, as indicated by the dotted radii. But as the spiral 



arrangement is continued up the stem and into the terminal bud, the leaves seem to 



themselves, as it were; so that the appearance of the spiral in the neighbour 

 ttood of the summit is more accurate than at the point of departure from the highest 

 pair ol opposite leaves. 



iii. La a similar manner to the above, direct transitions into the f arrangement 

 occurred cpute as often as into the |, the only difference being that the angle included 



between radii drawn to the pair of leaves which converge to one side is less than 150°, 



-mdeed, nearly, if not quite accurately, 135°, which is the angular divergence of the 1 



cement 



6 U1UI UUD1 5 



v >nly one instance occurred where opposite leaves were resolved in a similar way 

 dn e,lv .no he -ft. ^v hen this fraction was otherwise represented, it was dne to a slight 



ft' V6S " the CyCle foU0Win 8 "1™ ™ « -ore preceding cycles of the 



f di\ei ^once. o j 



II. TranMion. from tke v ccussate arrmgemcnt into ^^ ^ ^^ ^ 



pJ e I ^ ZT. " a <H " eCt tranSiti011 fr ° m the d " »*» 



the \ arrangement 



Alt houirli two pairs of decussate leaves are at ri*ht n™l ♦ 

 have an angular divert -nee of 90° or ' f " • ' and therefore > if projected on a plane, 



•ueh as is required for the I arrangement, £t ™U ZT^ ^ ^^^ ** "^ ° f the IeaVea C0Uld n0t ^ 



2 



5 



3 8 7 4 



6 



1 



tricuaiate leaves, as will be 



illust 



