CLASS DIDYNAMIA. 



165 



LECTUKE XXXI. 



DIDYNAMIA. TETKADYNAMIA. 



235. These two classes are foimded upon the mtmher and 

 relative length of the stamens. In distinguishing their orders, 

 the numher of styles is not regarded, but new circumstances of 

 distinction are introduced, viz., the seeds heing inclosed in a 

 pericarp^ or destitute of this covering^ and Fig. 144. * 



the comparative length ofj)ods. 



CLASS XIII.- 



-DIDYNAMIA, TWO PAIES OF 

 STAMENS. 



236. This class has flowers with four 

 stamens, arranged in pairs ; the outer pair 

 being longer, the inner pair shorter and 

 converging. It contains two orders, Gym- 

 nospermia (seeds naked or without a 

 j)ericarp), and Angiospermia (seeds in- 

 closed in a pericarp). The great natural 

 family of the Lahiateoe are mostly to be 

 found here ; the flowers are monopetalous and irregular in their 

 outline, labiate^ or hilahiate^ as the two-lipped corollas are some- 

 times called. Labiate flowers are divided into ringent^ gaping, 

 Siiid perso?iate^ masked or closed. These terms have been used 

 in an indefinite manner. Linnseus called the whole tribe riTi- 

 gent; these he subdivided into labiate and personate. This divi- 

 sion is illogical, since the specific term lahiate^ having lips, has 

 a more general signification than the generic term ringent^ lips 

 gaping. 



a. A few of the labiate flowers having but two stamens, are placed in the class 

 Diandria, as the sage and mountain mint. Yet they have, besides tlieir two per- 

 fect stamens, the rudiments of two others, as if nature had designed them for 

 didynamous plants. Linnaeus remarks, that the insects most fond of frequenting 

 these plants have but two perfect loings ; while the rudiments of two other wings 

 may be found concealed under a little membrane : — " How wonderful," he says, 

 " are the sympathies of nature !" When we examine a labiate flower, as balm or 

 catmint, we perceive that the arched upper lip of the petals covers the stamens, 

 and the lower lip hangs down, so that we can see the inside of the corolla ; by 

 drawing out the corolla, we find the stamens attaclied to it, as they usually are to 

 monopetalous corollas ; the corolla shows an aperture at the base" which had con- 

 tained the pistil. 



6. The labiate plants inhabit hills and plains exposed to the sun. They are des- 

 titute of any deleterious secretions. The aroma which escapes from their floA\ ers 

 denotes their stimulating medicinal properties. Their action upon the aninud 

 economy differs according to the quantity of essential oil and of bitter principle 

 which they contain ; when the former prevails, as in mint, they are aromatic and 



235. Classes Didynamia ami Tetrarlynamia.— 23r«. Orders of tho class Didynamin— Labiate planu<- 

 How divided 1 — a. Are all labiate tlowers in the class Didynamia ? — *. Properties of these plants. 



