88 THE FLOWERING PLANT. 
growth at the junction of the two, which is termed a ligule from 
its resemblance as regards position to the structure of that name 
in grasses. The ligules are collectively called the corona. One 
or more petals of the polypetalous corolla may be saccate or 
spurred. In the pansy and violet the lower petal is produced 
into a large spur (fig. 51). 
Wy! Larkspur and monkshood 
Se fats. (p. 85) have two spurred 
Zeus % petals, while all five petals 
Qu’ } have conspicuous spurs in 
the closely allied colum- 
bine, where the corolla is 
regular. A very common 
and striking form of zrre- 
gular corolla with free 
petals 1s seen in gorse, pea, 
Fic. 41—Petal of Fra. 42.—Sweet Pea, «, Dean, wistaria, clover, &c. 
Binks 2. limb 5) 0: calyx; e. standard; a. It has been termed papl- 
claw. wings; 0. keel. lionaceous. or butterfly- 
shaped (fig. 42). The odd posterior petal is here larger than the 
rest, and bemg somewhat upright, is known as the standard 
(veatllum). In front of this come a fairly large pair of petals, 
the wings (ale), which overlap a third smaller pair that are 
united into a boat-shaped structure, the keel (carzna), enclosing 
the stamens and pistil. The union of the last two petals is not 
complete, for they have separate stalks, nor is it very close, 
as they can readily be separated. Petals, like sepals, may be 
spreading or refleced, and when they are clawed the limb may 
be bent sharply on the claw. Thus, in the wallflower there are 
four equal petals, diagonal in position, and with long claws. 
The limbs spread abruptly out transversely to the claws, and the 
corolla is strikingly cross-shaped in consequence, for which reason 
it is termed cruciferous. 
Some of the most remarkable forms of irregular corolla are 
found in orchids, especially tropical ones. Perhaps the com- 
monest British species is the early purple orchis (Orchis mascula), 
which flowers from April to June. There are here three petaloid 
sepals, an upper one, arching over the central structures, and 
two spreading or reflexed lateral ones. Alternating with these 
are three other purple flower leaves, two smaller upper petals, 
arching like the upper sepal, and a much larger three-lobed one, 
the dabellum. The central lobe of this last is regarded as the 
lower petal, and the two side lobes as petaloid stamens fused with 
it. These conclusions are based upon comparison with allied but 
less modified plants and the structure of the parts. Details would 
