The Climbing Habit in Antirrhinum majus. 293 
four miles distant. A number of these were in time planted out in 
different positions in the garden, but owing to the check received in 
transplanting, together with the cold, unfavourable season, very 
few lateral branches of suitable length have developed and none of 
these plants have as yet flowered. A few left over in the frame, 
however, fared better, and one of these was well in flower during 
the latter part of September. A portion of this plant (the white 
flowered variety) is shown in the photograph, PI. III., Fig. 2. Just 
below the centre of the photograph, one of the branches may be 
seen which has formed a perfect coil around the stem of an adjacent 
Antirrhinum plant, which it is gripping firmly. 
Histology of a Twining Shoot. 
Another question that remains to be considered is :—Do these 
twining branches which so closely resemble in form and behaviour 
those of typical twiners, show any of their histological characteristics? 
Twining branches after being hardened in alcohol were sectionised 
both by hand and microtome. 
PI. IV., Fig. 1 is a photo-micrograph of a transverse section of 
a coiled branch. We see at once the close resemblance of this to 
the section of a typical twiner, such for example as is figured by 
Darwin. 1 The lower part of the section is the concave side, the 
upper part the convex side of the coil. 
The tissues on the concave side are seen to be more compact; 
both epidermal and cortical cells are smaller than those of the 
convex side, and modifications will also be noticed in the tissues of 
the stele. 
A comparison of coiled and uncoiled stems shows the following 
differences in the dimensions of the tissues:— 
Diameter of Diameter of Width of Width of 
Stem. Pith. Cortex, Cortex, 
Convex side. Concave side. 
Coiled Stem ... P590mm. '705 mm. *385 mm. '190 mm. 
Uncoiled Stem P695mm. '940 mm. *255 mm. '255 mm. 
Thus in stems of about equal diameter the twining stem has:— 
1. A smaller pith. 
2. A denser and narrower stele. 
3. Cortex on convex side, '130 mm. broader than normal. 
4. Cortex on concave side, -065 mm. narrower than normal. 
Thus the excess of radial thickening on the convex side is about 
double the radial compression on the concave side. 
1 C. Darwin. Movements and habits of climbing plants, 1875, 
p. 74. 
