248 EXPLANATION OF THE 



are indispensable to the production of fertile seed. It 

 is exemplified in the Garden Marygold. ha and Po- 

 lymnia are American genera. 



The fifth order, (Segregata) has its florets enclosed 

 in a partial calyx, and all included in one general calyx. 

 It is associated with the preceding orders by its united 

 anthers, but distinguished with facility by the calyx, 

 which is inferior, and not like the chaffy pappus supe- 

 rior to the seed. Globe Thistle and Elephantopus are 

 the only examples to which we can refer. This class 

 includes the compound flowers, which are particularly 

 abundant in the United States. The orders are with 

 some difficulty distinguished by the inexperienced bot- 

 anist, but the common calyx, the pappus, and the re- 

 ceptacle furnish abundant marks for distinguishing the 

 Genera. 



The class Gynandria, with stamens or sessile anthers 

 united to the pistil, has seven orders ; only four of 

 which occur in the United States. In the first, we 

 find the Orchidecs of Jussieu, wh@se glutinous pollen 

 is found in yellow masses, pollinia, enclosed in two 

 antheroid cells ; and these cells are either contigu- 

 ous or removed from each other to the opposite sides 

 of the style. The best division of the Orchidece is 

 founded on the structure of the anther, " which is 

 sometimes parallel to an unadhering stigma, and fixed, 

 and permanent, at others, crowning the column, and 

 generally moveable, lid-shaped and deciduous."* 



Some writers regard the column merely as a style, 

 but Mr. Brown describes it as formed by the incorpo- 

 ration of this organ with three filaments, two of which 

 are usually sterile, as in Orchis. 



In the second order (diandria) we find Cypripedium 

 * Journal of Science, &c. 



