BOTANY. 37 
extremity. The cotyledons, however, are not always of the same size, and 
the union between the two may be so intimate as to give rise to the pseudo- 
monocotyledonous embryo. Sometimes there are more than two cotyledons, 
and plants in which this occurs are sometimes termed polycotyledonous. Co- 
tyledons are usually entire and sessile. Sometimes, however, they become 
lobed as in the walnut, petiolate, or auriculate. Like leaves in the buds, coty- 
ledons may be either applied directly to each other, or else folded in various 
ways, becoming conduplicate, reclinate, convolute, circinate, &c. 
The radicle may be either straight or curved, the difference in this 
respect characterizing certain divisions of plants. Thus, in Cruciferz the 
division Pleurorhizeze exhibits the cotyledons applied by their faces, with the 
radicle folded along their edges, so as to be lateral ; the cotyledons are then 
accumbent. In Notorhizee the dorsal radicle is folded on the back of the 
incumbent cotyledons, these being applied to each other by their face. In 
Orthoplocez the cotyledons are conduplicate, and the radicle included between 
their folds. 
With respect to the perisperm, the embryo is infernal or intrarius when 
inclosed by this on all sides, excepting the radicular extremity ; when lying 
outside of the perisperm, and only coming in contact with it at certain points, 
the embryo is external or extrarius. When the embryo follows the direction 
of the axis of the seed, it is axile or axial, and may be either internal or 
external. When the embryo is not in the direction of the axis, it is abawial. 
When, as in some campylotropous ovules, the embryo is curved and external 
to the perisperm, it is peripherical. 
Although the radicle is usually turned towards the micropyle, and the 
cotyledons to the chalaza, yet the former may be directed to one side of the 
nucleus, and the embryo is then excentric. The position of the embryo in 
different seeds varies. In an orthotropal seed the embryo is andtitropal, the 
radicle pointing to the apex of the seed; if the nucleus be inverted or 
antitropal, the embryo will be erect or orthotropal. In curved seeds the 
embryo is folded, so that the extremities are approximated, hence called 
amphitropal. 
When a seed begins to germinate, the embryo first lengthens its radicle, 
then its caulicle, and afterwards sends the plumule upwards, in the form of 
a stem and leaves. The radicle extends downwards, either directly from the 
base of the embryo, or after having previously ruptured the integument of 
the base. Plants with the first character are said to be exorhizal ; with the 
second, endorhizal. 'The former is most common in dicotyledons ; the latter, 
in monocotyledons. In most plants the cotyledons are gradually raised to 
the surface by the growth of the caulicle, after which they become green 
and act as leaves ; sometimes, however, the cotyledons remain inclosed within 
the testa. 
f. Reproductive Organs of Flowerless Plants. 
We have already adverted in brief terms to many of the peculiarities of, 
37 
