LESSON 10.] AlIKANr.r.MKXT OF LKAVKS. 71 



LESSON X. 



Tin: AnRANr.r..Mi;.\T or lkavks. 



180. UxniiK tills hciid wo ni;iy roii>i(lcr, — 1. (he arranpemont of 

 leaves on the stem, or what is sotnetimes called rnYLLOTAXV (from 

 two Greek words meaiiiii;^ leaf-order) ; and 2. the ways in which 

 they are packed together in tin; bud, or their vkknatkjn (the word 

 meaninji their spring state). 



ISl. Pliyllotaxy. As already explained (18, 49), leaves are ar- 

 ranged on the .stem in two princijjal ways. They are either 



Alternate (Fig. 131, 143), that is, one after another, only a single 

 leaf arising from each node or joint of the stem; or 



Opposite (Fig. 147), when there is a pair of leaves on each joint 

 of the stem ; one of the two leaves being in this case always situ- 

 ated exactly on the opposite sid(; of the stem from the other. A 

 third, but uncommon arrangement, may be added ; namely, the 



Whorleil, or rerlicillale (Fig. 148), when there are three or more 

 leaves in a circle (trhorl or verticil) on one joint of stem. But this 

 is only a variation of the opposite mode ; or rather the latter ar- 

 rangi-ment is the same as the whorled, with the lunuber of the 

 leaves reduced to two in each whorl. 



182. Only one leaf is ever produced from the same point. When 

 two are borne on the same joint, they are always on opposite sides 

 of the stem, that is, are separated by half the circumference ; when 

 in whorls of three, four, five, or any other number, they are equally 

 distril)uted around the joint of stem, at a distance of one third, one 

 fourth, or one fifth of the circumfer- 

 ence from each other, according to 

 their number. So they always liave 

 tlie greatest jjossible divergence from 

 each other. Two or more leaves be. 

 longing to the same joint of stem 

 never stand side liy siilc, or one 

 aljove the other, in a clii-tcr. 



183. A\ iiat are called clustered or fnsricled leaves, and which 



Fl(i. 139. C'lustrrpil ur faxciclvil leaves of tlio L.-irch 



