CLASS DIDYNAMIA. 
l05 
LECTUEE XXXI. 
DIDYNAMIA. TETRADYNAMIA. 
235. These two classes are founded upon the nmriher and 
f elative length of the stamens. In distinguishing their orders, 
t te number of styles is not regarded, but new circumstances of 
distinction are introduced, viz., the seeds heing inclosed in a 
pericarps or destitute of this covering^ and 
the comparative length of pods. 
CLASS XIII. DIDYNAMIA, TWO PAIRS OF 
STAMENS. 
230. 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 
pericarp), and Angiospermia (seeds in- 
closed in a pericarp). Tlie great natural 
family of the Lahiateos are mostly to be 
found here ; the flowers are monopetalous and irregular in their 
outline, labiate^ or hilabiate^ as the two-lipped corollas are some- 
times called. Labiate flowers are divided into ringent^ gaping, 
and personate^ masked or closed. These terms have been used 
in an indefinite manner. Limigeus called the whole tribe rin- 
gent; these he subdivided into labiate and personate. This divi- 
sion is illogical, since the specific term labiate^ having lips, has 
a more general signification than the generic term ringent^ lips 
gaping. 
a. A few of tke labiate flowers having but two stamens, are placed in the class 
Diandria, as the sage and mountain mint. Yet they have, besides their two per- 
fect stamens, the rudiments of two others, as if nature had designed them for 
didynamous plants. Linnseus remarks, that the insects most fond of frequenting 
these plants have but two perfect wings ; 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 attached to it, as they usually are to 
monopetalous corollas ; the corolla shows an aperture at the base which had con- 
tained the pistil. 
b. The labiate plants inhabit hills and plains exposed to the sun. They are dea 
titute of any aeleterious secretions. The aroma which escapes from their flowers 
denotes their stimulating medicinal properties. Their action upon the animal 
economy differs according to the quantity of essential oil and of bitter priuviple 
ffhidi they contain ; when the former prevails, as in mint, they are aromatic and 
Fig. 144. 
235. Classes Didynamia and Tetradynamia. — 236. Orders of the class Didynamia— Labiate plania 
dovf divided ? — a. Are all labiate flowers in the class Didynamia 1 — b. P'operties of these plants. 
