The Climbing Habit in Antirrhinum majus. 295 
as a result of increased compression, while the walls of the cortical 
cells have increased greatly in thickness and show well-marked 
pits in their walls. 
Text-fig. 37, B, shows the thin walled outer tissues on the 
convex side of the same section. 
In following these thickened elements round towards the 
convex side it was found that they disappeared first from the outer 
cortex and last in those cells adjacent to the endodermis. 
A • B 
Text-fig. 37. A. T. S. of an older coil showing extent of thickening of 
cell walls in the outer tissues on the concave side. B. Convex side of same 
section as A, showing the thin walled tissues. 
This thickening extends to the stele, and the pericycle becomes 
strongly sclerenchymatous, but only on the concave side. Consider¬ 
able increase also occurs in the vascular tissues. This will be 
evident on comparing Figs. 2 and 3, PI. IV. Fig. 2 shows the stelar 
tissues on the convex side, and Fig. 3 shows the stelar tissues on 
the concave side of the same section. It will also be noticed in the 
latter figure that considerable secondary growth has taken place on 
the concave side, in strong contrast to its weak development or 
absence on the convex side. 
The first perceptible change in structure is a slight difference 
in width of the cortex. This appears as a flattening, probably due 
to loss of turgescence and consequent contraction of the cells on 
the concave side. On this slightly flattened narrow side, the 
epidermis thickens, first on the outer wall, then on the inner, and 
finally on the lateral walls. No trace of thickening in the cortex 
can as yet be seen. 
