156 Saunders. — The Leaf -skin Theory of the Stem: 
above, p. 140, and Fig. 15). In the flower spike the arrangement changes 
to a f divergence with a bract-insertion width of J, the eight contour lines thus 
produced being continued uninterruptedly along the axis (see Figs. 13 and 
16). On the individual flower stalks from five to eight lines demarcating 
the downward extensions of a corresponding number of sepals are plainly 
visible. 
Cytisus purgans. Leaf-divergence §, leaf-insertion width about -J. 
With this combination we should ordinarily expect a continuous five-line 
configuration, but here we find ten lines (see Fig. 31). This doubling of the 
Figs. 32 - 33 . 32 , Hedera Helix , seedling plant; a dicotyledon type with circular leaf-in- 
sertion. 33 , Tinanlia fngax, a monocotyledon type with a conspicuous line of hairs along the 
line of fusion of the edges of the tubular sheath and of the leaf-extension ; cotyledon apex withered. 
contours is due to the fact that in this species the free portion of the leaf is 
reduced to two small paired membranous flaps, and the five additional lines 
arise at their point of junction. The appearance that these membranous 
flaps would readily peel off, bringing away a longitudinal green strip beneath 
them, is suggestive of that actuality which in its more pronounced form, 
when the leaf is obviously decurrent, is universally recognized. 
Hedera Helix. Leaves spiral. In the seedling it can be seen that the 
leaf has an insertion which completely embraces the axis, hence each inter- 
node is entirely covered with the downward extension of a single leaf (see 
