30 VEGETABLE PHYSIOLOGY 
going round either the whole axis or separate parts of it. 
The first of these regions is the layer underlying the 
tegumentary tissue, which the new development sup- 
plements and strengthens. Most moss plants show the 
hypodermal cells of their axis thickened, while such a 
development is very common in many petioles and leaf- 
blades. The new development may occur in close relation- 
ship with the vagcular bundles, which, in such cases, are 
found among large-celled somewhat succulent parenchyma, 
Fia, 29.—Transverse Section or RuizoMe oF TUB BRAVKEN FERN. 
x 10. 
sc, bands of soleronchyma; hy, hypodermal sheath of sclerenchyma ; 
st, steles; ep, epidermis, 
and are not generally very strongly developed. The scler- 
enchyma by forming a separate sheath round each bundle 
gives it a rigidity which it could not derive from its own 
elements, and in addition prevents the whole stem from 
beimg crushed. This arrangement is seen in the stems of 
many semi-succulent monocotyledonous plants, such as those 
of the maize and the asparagus (fig. 81). The sclerenchyma 
may also occur freely in the ground tissue, at some distance 
from both tegumentary and vascular structures. The bands 
of it which occur in the rhizome of the bracken fern are 
good illustrations of this mode of disposition. The two 
