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 



the front lower petal is large and 



spurred at its base, the side petals 



are smaller, while the back petals are 



larger. There is an unlikeness in the 



, ,, a . ... 1,1 Fio. 175. Viola. 



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 



FIG. m.-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, 



