296 Dr. Lindley’s Natural System of Botany. 
ter to the inside of their stem near the centre ; those are Endogens. 
But Exogens have two or more cotyledons to their embryo, and 
hence are called Dicotyledons ; while Endogens have only one co- 
tyledon, and are, therefore, Monocotyledons. Exogens have the 
young external wood connected with the centre by medullary pro- 
cesses; Endogens having no occasion for such a provision, are des- 
titute of it. In Exogens the leaves have their veins disposed in a 
netted manner; in Endogens the veins run parallel with each other. 
The number of parts in the flower of an Exogen is usually five, or 
its multiples; in an Endogen it is as usually three, or its multiples. 
In germination the young root of Exogens is a mere extension of the 
radicle ; but of Endogens it is protruded from within the radicle ; 
hence the former have been named Evorhize, and the latter Endor- 
hize. In this case then, as in the last, we have two groups differing 
entirely from each other in their germination, the structure of their 
stem and leaves, their mode of growth, the arrangement of the parts 
of the flower, and in the organization of their embryo. It is impos- 
sible, therefore, not to recognize such groups also as natural. 
«To this separation of the vegetable kingdom into Exogens, En- 
dogens, and Acrogens, or by whatever synonymous names these 
groups may be known, many botanists confine themselves. But 
there are two others, of subordinate importance perhaps, but never- 
theless characterized by circumstances of a similar nature, and, there- 
fore, I think, to be esteemed of equal dignity with them. In true 
Exogens and Endogens, the fertilizing principle is communicated to 
the young seeds through the medium of a stigma which terminates 
a case or pericarp in which they are enclosed. But in some plants 
otherwise Exogens, the. fertilizing principle of the pollen is applied 
immediately to the seeds, without the intervention of any pericarp- 
ial apparatus, and they bear the same relation to other Exogens as 
frogs and similar reptiles to other animals. These plants, therefore, 
are separated as a distinct class, under the name of Gymnosperms. 
Like the other groups of the same grade, these are also found to 
possess peculiarities of a subordinate nature. For instance, they 
have in many cases more cotyledons than two, whence they have 
been called Polycotyledons ; their radicle usually adheres to the al- 
bumen in which the embryo lies, and that circumstance has given 
Tise to the name Synorhize. The veins of their leaves, when they 
nay ae ae are either simple or forked; in which respect they 
bh Endogens on the one hand, and Acrogens on the other- 
