AXIS FLOWERS 303 
pistil cavity, and the ovules grow upon these margins, 
i.e. the placentae (the areas from which the ovules grow) 
are ‘‘parietal.”” The stamens are 
five, the usually blue petals five and 
the green sepals five. In all violets Ly 
the front lower petal is large and All\) 
spurred at its base, the side petals 
are smaller, while the back petals are 
larger. There is an unlikeness in the 
petals, and the flower is “irregular.” 
554. The Mustard flower (Brassica) has reduced the 
number of its parts still further, the pistil being bicar- 
pellary. Its two carpels are united at their margins, and 
the ovules grow upon these margins (parietal placentae), 
as in the Violet. Here, however, a thin membrane 
stretches across from margin to margin dividing the cavity 
into two. The stamens are six in two whorls (4 and 2), 
the yellow petals four, and the green sepals four. All 
of these parts grow upon the very short flower axis. 
555. In some Pinks (Lychnis) the five-carpelled pistil 
has broken away the partitions between the carpels so 
that there is but one pistil cavity, 
although the five styles indicate its 
structure. The ovules grow upon a 
@& central column, the united placentae. 
The stamens are ten (two whorls), the 
Fic. 176.—Lychnis, petals five, and the united green sepals 
five (gamosepalous). In some other 
pinks the carpels are reduced to two, but the flowers are 
otherwise like those of Lychnis. 
556. The Primrose flower (Primula) reminds one of the 
pinks, but here the five petals have grown together into a 
tubular corolla, so that it is spoken of as gamopetalous. 
The pistil is composed of several (probably five) carpels, 
Fia. 175.—Viola. 
