48 



PHTLLOTAXY, OR LBAP ARKANGEMENT. 



ease of the subsequent developmont of the branch, as often occurs iu tho Berb- 

 eris and larch, their spiral arrangement becomes manifest In the pines the fas- 

 cicles have fewer leaves, their numberbeing definite and characteristic of thespeciea 

 Thug P. strobus, the white pine, has 5 leaves in each fascicle, P. palustris, the long- 

 leaved pine, has 3, P. inops, 2. 



226. The opposite leaved type is also spiral. Tho leaves in each circle, 

 whether two or more, are equidistant, dividing the eircamference of the stem into 

 equal arcs. The members of the second circle are not placed directly above those 

 of the first, but are turned, as it were, to the right or left, so as to stand over tha 

 intervening spaces. Hence there may be traced as many spirals as there are leaves 

 iu each whorl. 



22'7. Decussate leaves result from this law, as in the motherwort, 

 and all the mint tribe, where each pair of opposite leaves crosses in di- 

 rection the next pair, forming four vertical rows of loaves. Therefore, 

 it is 



228. An established law that the course of development in the 

 growing plant is universally spiral. But this, the formative cycle as it 

 is called, has several variations. 



92, 93, 94, showing the course of the spiral thread and tho order of the leaf-succession in ti c 

 axes of elm, alder, and cherry. 95, axis of Osage-orange with a section of tho barii paeled, di.s- 

 playing the order of the leaf-scars (cycle §). 



229. The elm otole. In the strictly alternate arrangement (elm, linden, grasses) 

 the spiral thread makes one complete circuit and commences a new one at the third 

 leaf The third leaf stands over tho first, the fourth over tho second, and so on, 

 forming two vertical rows of leaves. Here (calling each complete circuit a cycle) 

 we observe 



230. PlEST, That this cycle is composed of two leaves ; second, that the angu- 

 lar distance between its leaves is }■ a cycle (180°); third, if we express this cycle 

 mathematically by \, the numerator (1) will denote the turns or revolutions, the de- 

 nominator (2) its leaves, and the fraction itself the angular distance between the 

 leaves (J ofSOO"). 



