6 REVIEWS. 



processes ; Endogens, having no occasion for such a provi- 

 sion, are destitute 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 En- 

 dogen it is 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 Exorhizce, and the latter Endo- 

 rhizce. 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 arrangements of the parts of the flower, and in the or- 

 ganization of their embryo. It is impossible, therefore, not 

 to recognize such groups also as natural. 



" To this separation of the vegetable kingdom into Ex- 

 ogens, Endogens, and Acrogens, or by whatever synonymous 

 names these groups may be known, many botanists confine 

 themselves. But there are two others, of subordinate im- 

 portance, perhaps,- but nevertheless characterized by circum- 

 stances of a similar nature, and therefore, 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 termi- 

 nates a case or pericarp in which they are inclosed. But in 

 some plants otherwise Exogens, the fertilizing principle of 

 the pollen is applied immediately to the seeds, without the 

 intervention of any pericarpial 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 pos- 

 sess 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 albumen 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 



