Tissues in Certain Monocotyledons. 41 
sions, in one case measured, the thickening had become purely 
cortical at a distance of 1-3 cm. from the nearest part of the 
base of the branch-root. The length of the region of transi- 
tion renders it inconvenient to figure on an adequate scale ; 
consequently we have contented ourselves with reproducing 
a corresponding transverse section (Fig. 7), to which we shall 
return. 
If a transverse section be taken at some distance from 
a lateral root (say 1-1*5 cm - above or below), only cortical 
secondary tissues are shown. They may extend all round the 
cylinder or be limited to the side on which the lateral root is 
situated ; that depends on the amount of progress which the 
thickening has made. In any case, however, the zone is 
thicker on the side corresponding to the branch-root. If the 
transverse section be made nearer the latter, we find both 
pericyclic and cortical secondary growth at one side, which as 
it thins out to the right and left becomes purely cortical (see 
Fig. 4). Lastly, if the section pass through, or close to the 
insertion of the lateral root, we find pericyclic thickening next 
the insertion, and cortical at a distance from it, with a more or 
less gradual transition between them. There are many varia- 
tions in detail, of which Fig. 4 and Fig. 7 will give some idea ; 
Fig. 5 is from a region of purely cortical thickening, at 
a distance from a lateral root, while Fig. 6 is from the 
transitional region. In Fig. 7 the transition is unusually 
sudden, causing a sharp break in the endodermis, reminding 
one of a geological ‘ fault.’ 
If our sections be cut from comparatively young roots, we 
find only the pericyclic thickening near the base of the lateral 
roots. It thins out altogether at a distance from them, and 
the cortical thickening has not yet begun. 
It may be worth while to mention that in one large root, 
2 -i cm. in diameter, where the secondary tissues extended 
round the whole circumference, their maximum thickness, 
on the side towards the lateral root, was 3*5 mm., the mini- 
mum thickness, on the side opposite the lateral root, was *5 mm. 
In this case there was some pericyclic thickening all the way 
