ROOT OF CORMOPHYTES. 135 
the coleorhiza, co. Such a mode of root-development has been 
termed endorlizal. The roots of Monocotyledons are therefore 
to be regarded as adventitious or secondary. 
From their mode of development it rarely happens that the 
plants of this class have tap-roots, but they have instead a 
variable number of roots of nearly equal size (fig. 259), which 
are accordingly often termed compound. There are, however, 
exceptions to this, as for instance in the Dragon-tree (fig. 196), 
which has a descending axis resembling the ordinary tap-root of 
Dicotyledons. 
Aerial roots are much more common in Monocotyledons than 
in Dicotyledons. We have already referred to them in the 
Screw-pine (jig. 199, 2), and other plants of this class. In 
many Palms they are developed in great abundance towards the 
base of the stem, by which this portion assumes a conical appear- 
ance, which is at once evident by the contrast it presents to the 
otherwise cylindrical stem of such trees. In its internal struc- 
Bre. 259. 
Fie. 260. 
Fig. 259. Fibrous roots of a Grass. 
Fig. 260. Coralline root. 
ture the root of a Monocotyledon corresponds to that of the stem 
in the same class of plants. 
3. The Root of Cormophytes or Acrogens.—Such plants, as we 
have seen (page 11), have no true seeds containing an embryo, 
but are propagated by spores, from which roots are developed in 
a very irregular manner ; and hence this mode of root-develop- 
ment has been called heterorhizal. Such roots are therefore all 
adventitious ; and resemble those of Monocotyledons in being 
compound. When the stem has become developed it soon also 
gives origin to other aerial adventitious roots, by which such 
plants are often chiefly supported. Hence aerial roots are very 
common in Acrogenous plants, as they are in Monocotyledons ; 
indeed, in Tree-ferns, as in many Palms, these roots are so 
abundant at the base of the stem, that they sometimes double, 
triple, or still further increase its normal thickness (jig. 15, ra), 
and hence give to the lower part of such stems a conical form. 
