THE DICOTYLEDONES 1727 



3. Sclerantheoe. The flowers are all developed equally but the leaves 



are exstipulate and opposite. Scleranthus. 



4. Pterantheae. The flowers are in groups of three, the two lateral 



flowers being more or less abortive. Pteranthus. 



Bentham and Hooker separate the last four of these groups as a distinct 

 family, the Illecebraceae, but this now generally considered an unjustifiable 

 separation of related groups. 



H. Silenoideae 



In this sub-family the flowers are gamosepalous and hypogynous. The 

 petals are often red in colour and are differentiated into stalk and limb. 

 There is often an out-growth or ligule forming a corona in the flower. 

 The sub-family is divided into two groups. 



1. Lychnideae. The calyx has commissural ribs. Silene and Lychnis. 



2. Diantheae. There are no commissural ribs on the sepals. Gypsophila, 



Dianthus, Saponaria (Fig. 1602). 



Fig. 1602. — Saponaria officinalis. Flowers. 



A typical example of the Alsinoideae is the isomerous flower of Spergu- 

 laria arvensis, in which the five simple white petals are succeeded by two 

 whorls of five stamens, of which only one is sometimes developed, and five 

 carpels. In certain other genera such as Stellaria (Fig. 1603) the flower is 

 usually pentamerous but occasionally tetramerous and the carpels are 

 reduced to three, but considerable variation may occur within a single 

 species. 



