94 BRITISH FLOWERING PLANTS chap. 



leaves have broad bases and thus protect the bud in 

 their axil, there are no stipules, while on the other hand 

 where the leaves are narrow the bud is protected by 

 stipules. H. guttatum is a very instructive case. The 

 upper leaves have stipules, while the lower ones have 

 none. Now the lower leaves have broad leaf-bases, 

 which effectually protect the bud, and they are exstipu- 

 late ; the upper leaves, on the contrary, are narrow at 

 the base, but they are provided with stipules. The 

 reason for the presence or absence of stipules seems, then, 

 quite obvious, so far as the Rock Roses are concerned ; 

 and the evidence is strengthened by finding similar 

 relations in other genera. 



H. vulgare. — The flower is large and bright yellow. 

 Though producing no honey it is visited by a good 

 many insects for the sake of the pollen. 



H. polifolium. — In this species the stamens are 

 sensitive. They stand upright, but if touched bend 

 down to a horizontal position, slowly resuming their 

 original attitude in about fifteen seconds. 



H. canum. — The flower, according to Briquet, is 

 opened and closed by movements of the sepals. The 

 stamens are not sensitive. The flower is protogynous, 

 and as the anthers open outwards self-fertilisation is 

 almost excluded. The leaves are white underneath and 

 sometimes on both sides. 



POLYGALACEiE 



Chiefly tropical and southern. The only European 

 genus is Polygala, the Milkwort. 



P. vulgaris. — A variable species presenting several 

 forms often regarded as distinct, but from their varia- 

 bility considered by Bentham and Hooker to be A-arieties. 

 The two inner, coloured, petal-like sepals are termed 

 " wings." They give the flowers a papilionaceous aspect. 

 The petals form a tube to the inside of which the 



