MONOCOTYLEDONOUS EMBRYO. 343 
chink, will be observed on one side near the base ; and if a ver- 
tical section be made parallel to this slit, a small conical projec- 
tion will be noticed, which corresponds to the plumule: and 
now, by making a horizontal secticn, the cotyledon will be 
noticed to be folded round the plumule, which it had thus 
almost entirely removed from view, only leaving a little slit 
corresponding to the union of the margins of the cotyledon ; and 
which slit thus became an external indication of the presence of 
the plumule. In fact, the position of’ the cotyledon thus rolled 
round the plumule is analogous to the sheaths of the leaves in 
most Monocotyledonous plants, which thus, in 
a similar manner, enclose the young growing 
parts of the stem. 
In other monocotyledonous embryes the 
different parts are more manifest ; thus, in 
many Grasses, as, for instance, the Oat (fig. 
705), the cotyledon, c, only partially encloses 
the plumule, g, and radicle, 7; and thus these 
parts may be readily observed in a hollow space 
on its surface (jig. 704). 
We have already stated (page 342) that a 
monocotyledonous embryo has occasionally 
more than one cotyledon, in which case the 
cotyledons are always alternate, and hence such 
embryos are readily distinguished from those 
Fie.766. Fre. 767. 
of Dicotyledonous plants, where the cotyledons 
are always opposite to each other if there are 
but two (jig. 773), or whorled (fig. 772, c¢) 
when they are more numerous (page 344). 
The inferior extremity of the radicle is 
usually rounded (jig. 767, 7), and it is through 
this point that the rootlets, 7, burst in germina- 
tion (fig. 765). The radicle is usually much 
shorter than the cotyledon, and generally 
thicker and denser in its nature ; but in some 
embryos it is as long, or even longer, in which 
Fig. 766. Vertical 
section of a mature 
carpel of a species 
of Triglochin.  p. 
Pericarp. s. Stigma. 
g. Seed. 7. Raphe. 
J.Funiculus. c.Cha- 
laza.—Fig. 767. Em- 
bryo of Tv7iglechin. 
7 Radicle. 7. Slit 
corresponding to 
the plumule.  . 
Cotyledon. From 
Jussieu. 
case the embryo is called macropodous. 
(b) The I%cotyledonous Embryo.—These embryos vary very 
much in form : most frequently they are more or less oval, as in 
the Bean and Almond (jig. 768), where the embryo consists of 
two nearly equal cotyledons, c, between which is enclosed a 
small axis or tigellum, t, the upper part of which, g, is the plu- 
mule, and the lower, 7, the radicle. The tigellum upon ger- 
mination appears as a little stalk (fig. 18, t), supporting the 
cotyledons, and hence it is also termed the hypocotyledonary 
axis (see page 342). 
In by far the majority of cases the two cotyledons are nearly 
of equal size, as in the Pea (jig. 16, c, c) ; but in some embryos, 
as in Trapa, some Hirzas, Xe. (fig. 769, c’, c), they are very 
