88 STRUCTURAL BOTANY. 



Their arrangement on the axis is according to the following 

 general modes : 



Alternate, one above another on opposite sides, as in the Elm. 



Scattered, irregularly spiral, as in the Potato vine. 



Itosulate, clustered regularly, like the petals of a Rose, as in 

 the Plantain and ShepherdVpurse. 



Fasciculate, tufted, clustered many together in the axil, as 

 seen in the Pine, Larch, Berberry. 



Opposite, two, against each other, at the same node. Ex., 

 Maple. 



Verticillate, or whorled, more than two in a circle at each 

 node, as in the Meadow-lily, Trumpet-weed. We may reduce 

 all these modes to TWO GENERAL TYPES, the alternate, inclu- 

 ding all cases with one leaf at each node ; the opposite, including 

 cases with two or more leaves at each node. 



263. The true character of the alternate type may be learned 

 by an experiment. Take a straight leafy shoot or stem of the 

 Elm or Flax, or any other plant with seemingly scattered leaves, 

 and beginning with the lowest leaf, pass a thread to the next 

 above, thence to the next in the same direction, and so on by all 

 the leaves to the top ; the thread will form a regular spiral. 

 The opposite leaved type is also spiral, consisting of two or more 

 parallel spirals as many as there are leaves at the node. There- 

 fore it is 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 varieties. 



264. The Elm cycle. 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 the first, the fourth over the second, and so on, 

 forming two vertical rows of leaves. Here (calling each com- 

 plete circuit a- cycle) we observe, first, that this cycle is composed 

 of two leaves ; second, that the angular distance between its 

 leaves is \ a circle (180) ; third, if we express this cycle math- 

 ematically by , the numerator (1) will denote the turns or revo- 

 lutions, the denominator (2) its leaves, and the fraction itself the 

 angular distance between the leaves (^ of 360). 



265. The Alder cycle. In the Alder, Birch, Sedges, etc., 



