142 
Saunders . — The Leaf -skin Theory of the Stem : 
Figs. 15-23. 15, Reseda odorata, vege tative axis; leaf-divergence •§, leaf-insertion between 
it and §. 16, flowering axis of the same, leaf-divergence §, leaf-divergence approximately 
pedicel showing the sepal extensions. 17, Viola tricolor , showing contours of bract and sepal 
extensions, a. bract ; b, posterior sepal (the appendiculate portion has been cut away). 18-20, 
Calystegia dahurica. 18 (diagrammatic), stem viewed as if transparent, phyllotaxis as in Reseda 
(Fig. 15); 19, a, unopened flower-bud; b, contour lines from the bracts which have been cut 
away at c; d , channelled petiole; 20, after torsion. 21, Epilobium parviflorum \ cotyledons 
glabrous, hypocotyl ridge without hairs, leaf-petioles ciliafe, internodes with ridge line surmounted 
with hairs. 22-23, Lopezia coronata , showing the leaf-extension edges flanked with a line of hairs. 
22, lower region of the stem, leaves opposite ; 23, upper region, leaves spiral. 
