CLASS TETRANDRIA. 



137 



Fig. 133. 



natural family; tlie genera which compose it appearing little 

 united by natural relations. 



178. Order Monogynia^ one pistil. — 

 HousTONiA coeridea is known by differ- 

 ent common names ; as Innocence^ Ve- 

 Qius^s Pride., and Blue Houstonia. It is 

 a very delicate little flower, appearing 

 early in the spring, in grassy fields and 

 meadows ; the color varies from sky-blue 

 (which gives its specific name, cceriderr) 

 to pure white. It has a small calyx 

 with four sepals, and a monopetalous co- 

 rolla of four deep divisions, which gives 

 it the appearance of a cruciform plant. 



The common Plantain {Plantago., Fig. 133, a) is found here. 

 The flowers grow on a spike ; they are very small, but each one 

 has a calyx and corolla ; these are four-parted ; the fllaments 

 are long ; the pericarp ovate, with two cells. 



179. Aggregate Floioers.' — ^We find in this class what Linnjeus 

 called the aggregate flowers. This term is used when many 

 flowers are situated on the same receptacle ; they have a gen- 

 eral resemblance to the compound flowers in the class Syn- 

 genesia, but difler from them in having but four stamens, with 

 anthers separate, while the Syngenesious plants have flve 

 united anthers. The aggregate flowers are not often yellow 

 like many of the compound flowers, but are usually either 

 blue, white, red, or purple. The button-bush {CepJialanthus) 

 is a shrub of about five feet in hight. The inflorescence is white, 

 appearing in large heads of a globular form, each consisting of 

 many 2:>erfect little florets. Only one species of this genus, the 

 occidentalism/^ is known, and this is entirely confined to North 

 America. The Cor nits (from cornii^ a horn, so called on ac- 

 count of the hardness of the wood) is a genus composed mostly 

 of shrub-like plants with flowers growing in flat clusters, or 

 cymes. The florida^ a species of cornus called dog-wood, is a 

 beautiful ornament of our woods. It is from fifteen to thirty 

 feet in hight. Its real corollas are very small, but the head 

 or cyme is surrounded by an involucrum of four large ob- 

 ovate leaves, usually white, but sometimes of a pale rose- 

 color ; hence its specific name florida., or florid. The large 

 leaves of the involucrum might at first sight be regarded as 

 petals. At Fig. 133, J, is a representation of a species of the 

 comus; the style is about the same length as the petals; 



• From occidens, the west, being found on the western continent. 



178. First order— Iloustonia— Plantain.— 179. Aggregate flowers— Button-bush— Cornufc • 



