PHYLIOTAXY, OE LEAF-ARRANGEMENT. 



47 



221. Position upon the stem. Leaves are radical when they grow- 

 out of the stem at or beneath the surface of the ground, so as to appear 

 to grow from the roots ; cauline when they grow from the stem, and 

 ramial {ramus, a branch), when from the branches. 



222. Insertion upon the axis. The arrangement of the scales 

 and young leaves in the bud appears to be in close, contiguous circles. 

 By the development of the axis the leaves are separated, and their order 

 variously modified, 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. 



Rosulate, clustered regularly, like the petals of a rose, as in the 

 plantain and shepherd's-purse. 



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 



223. Two GENERAL TYPES, — the alternate, including all cases with 

 one leaf at each node, — the opposite, including cases with two or more 

 leaves at each node. 



224. 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. 



225. PasoiCulate leaves are the members of an undeveloped branch, and in 



Phyllotaxy. 89, lenfy branch of elm,— cycle }. 90, leafy branch of alder,— cycle 4 ; 91, leafy 

 branch of cherry, — cycle j. 



