U1 - U', leaf-traces, numbered according to the phyllotaxis, It 5 belonging to the lowest leaf of the five; ph, a group of primary phloem; pd, periderm, formed from pericycle.
- The genus Lepidodendron, with very numerous species, ranging from the Devonian to the Permian, consisted of trees, with a tall upright shaft, bearing a dense crown of dichotomous branches, clothed with simple narrow leaves, ranged in some complex spiral phyllotaxis.
Divergence may alter either a, The branch, with the leaves abruptly or gradually, and the numbered in order; b, a magnified phyllotaxis thus becomes very representation of the branch, complicated.
In the bud of the screw-pine the leaves are arranged in three orthostichies with the phyllotaxis but by torsion the developed leaves become arranged in three strong spiral rows running round the stem.
These causes of change in phyllotaxis are also well exemplified in the alteration of an opposite or verticillate arrangement to an alternate, and vice versa; thus the effect of interruption of growth, in causing alternate leaves to become opposite and verticillate, can be distinctly shown in Rhododendron ponticum.
In different species of the same genus the phyllotaxis frequently varies.
- Diagram of a phyllotaxis); and the fourth in those of the silver fir.
It has been found in general that, while the number 5 occurs in the phyllotaxis of Dicotyledons, 3 is common in that of Monocotyledons.