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 Exorhizcc, and the latter Endor- 

 hizfc. 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 Poly cotyledons ; their radicle usually adheres to the al- 

 bumen in which the embryo lies, and that circumstance has given 

 rise to the name Synorhiza. The veins of their leaves, when they 

 have any veins, are either simple or forked ; in which respect they 

 approach Endogens on the one hand, and Acrogens on the other. 



