

PRELIMINARY DISCOURSES. XXXV 



The third division includes those in which the Corolla (and 

 occasionally the Calyx, also,) is wanting ; and the plants of this 

 division are therefore called apetalous Exogens. A few exceptions, 

 however, occur in each of these divisions (as in every other arrange- 

 ment, yet devised whether natural, or artificial) ; which will be 

 noticed in the proper places. 



The Subclass of Gymnosperms as already mentioned consists 

 of a couple of Orders ; viz. the Coniferae, or Pine Family, and the 

 Cycadaceae a small tropical Order, in which the pistil is repre- 

 sented by an open scale, or by a more evident leaf, or sometimes 

 entirely wanting ; and the ovules and seeds consequently naked i. e. 

 not included in a pericarp. 



The above are the principal divisions of the great Class of 

 Exogenous Plants: But these (as in the other Classes,) are again 

 sub-divided into Groups, Orders, Suborders, Tribes, Subtribes, Genera, 

 Subgenera, Species, and Varieties. The Groups comprise kindred 

 Orders, while the Orders and Tribes consist of kindred Genera, and 

 usually derive their names from some well-defined typical Genus 

 (as Malvaceae, or Rosaceae),- or some characteristic family feature 

 (as Umbelliferae, or Leguminbsae).* 



The Class of Endogens partially defined above does not admit 

 of so many principal divisions, as the preceding ; but contains a 

 number of well-characterized Orders and Tribes, as will be seen in 

 the following pages. 



The second or lower SERIES of plants called cryptogamous, or 

 fiowerless has been divided into three Classes ; in two of which, the 

 plants have a distinct axis, or definite stem and foliage, and in the 

 third, there is no distinction of stem and foliage, but a mere veget- 

 able expansion or thallus, so called. The plants of the first of 

 these cryptogamous Classes, consist of woody and vascular tissue, 

 and grow only at the summit, and are, for that reason, termed 

 Acrogens, or Apex-growers, embracing the Ferns, and Fern-like 

 plants. Those of the second Class consist of cellular tissue only ; but, 

 having a distinct foliage, and acrogenous growth, with somewhat of 



* Some of the Orders are so remarkably natural i. e. the structure and more 

 obvious features of the plants comprised by them, are so similar, that it is often 

 difficult to indicate good and striking characteristics, by which to distinguish the 

 {/ewera belonging to them. This is especially true of the Families named Oruci- 

 J'erae, Umbelliferae, and Labiatae: so much so, indeed, that each of those Orders 

 might be regarded as a comprehensive, and yet tolerably well-defined, Genus. 

 This fact will enable the Student to understand why it has been found necessary, 

 in such families, to seize upon any constant characters however minute, or 

 obscure that may eenre to discriminate between closely allied Tribes and 

 Genera. 



