6ao 
PHANEROGAMS. 
and pushes the end of the root, together with the plumule which is enveloped 
by the sheath of the cotyledon, out of the seed (Fig. 419), while its upper part 
remains in the endosperm as an organ of absorption, until the endosperm is 
consumed. In Grasses, however, the whole of the plumule projects from the seed, 
the scutellum only remaining behind in it, in order to convey to the embryo the 
food-material contained in the endosperm. 
The growth of the primary root of Monocotyledons soon ceases even when 
it is very strongly developed during germination, as in Palms, Liliacese, Zea, &c.; 
lateral roots are produced in its place, springing from the axis, which are stronger 
the higher up they are produced on it. No such permanent root-system is 
developed from the primary root of Monocotyledons as is found in Gymnosperms 
and in many Dicotyledons ; sometimes no roots at all are produced, as in some 
Orchidaceous saprophytes destitute of chlorophyll (as Epipogium and Corallorhiza), 
which never possess any roots. 
The plumule of the embryo is usually completely enclosed in a single 
sheath-like structure, the first leaf or cotyledon, which developes either into a 
sheath-like cataphyllary leaf or at once into the first green foliage-leaf of the 
young plant (as in Allium). Within the cotyledon there is generally a second 
and sometimes (in Grasses) a third and fourth leaf, which protrude on germination 
out of the sheath of the cotyledon, increasing by intercalary growth at their base ; 
these and the leaves which are formed subsequently are larger the later they are 
formed on the growing axis. The axis usually remains very short during germi- 
nation without forming any distinct internodes {Allium, Palms, &c.), or it lengthens 
more rapidly and becomes segmented into evident internodes {Zea and other 
Grasses). 
The increase in strength of the plant may take place by the powerful growth 
of the axis of the embryo itself, so that this at length forms the primary stem 
of the mature plant bearing the organs of reproduction, as for instance in most 
Palms, Aloes, Zea, &c. If the axis of the embryo remains short while it increases 
in strength, it may grow considerably in thickness and form a tuber (Fig. 420), 
or, if the bases of the leaves become thick (as in Allium Cepa), a bulb. If the 
axis of the embryo itself developes into the primary stem, whether into an upright 
one or a creeping rhizome, it first of all takes the form of an inverted cone, which 
is elongated or abbreviated according to the length of the internodes. This 
peculiarity, which belongs to most Monocotyledons in common with Ferns, depends 
on the absence of any subsequent increase in thickness ; the portions of the stem 
first formed retain their size, while each successive portion is larger ; the diameter 
of the stem is therefore so much larger the nearer it is taken to the apex. As 
long as this growth proceeds, the stem continues to grow stronger ; but sooner 
or later there comes a time when every portion of the stem acquires the same 
thickness as the previous one ; the stem then becomes cylindrical, or, if it is 
compressed like some rhizomes, still with a uniform breadth. The lateral shoots 
exhibit the same peculiarity when they spring low down from the primary stem 
(as in Aloe, &c.). But the primary shoot which springs from the embryo not 
unfrequently disappears after producing lateral shoots which grow more vigorously 
than it, and these again transfer the further growth to new shoots, which now 
