334 



THE LOWER DICOTYLEDONS. 



flower-bud is protected by the petals, which are at first 

 curved inwards. When the flower opens, by the outward 

 curving of the petals, each stamen curves outwards and 

 sheds its pollen ; later, the stigmas separate and spread out, 

 ready to receive pollen; finally, the stamens bend inwards 

 again. Thus, though the flower is protandrous, self-polli- 

 nation may occur as a last resort if the flower has not been 

 pollinated while the stamens were bent outwards. 



The flowers are visited by insects of all kinds, the honey 

 being freely accessible to flies and beetles with short tongues. 

 The large flat- topped inflorescence is very conspicuous, though 

 the individual flowers are small, and the massed effect is 

 heightened by the fact that the outermost flowers those 

 around the edge of the whole inflorescence have their 3 

 outer petals larger than the 2 inner ones, and are therefore 

 zygomorphic (cf. Candytuft and some other Crucifers). 



PETAL 



OVARY 

 {INFERIOR) 



Fig. 135. Vertical Section and Floral Diagram of Flower of Cow Pai-snip. 



After pollination, the petals and stamens drop off, and the 

 ovary develops into a flat dry fruit, which eventually splits 

 into 2 parts (mericarps, i.e. "divided fruits"), which are 

 suspended on the 2 branches of a Y-shaped stalk (carpophore, 

 i.e. "fruit-carrier"). Each half -fruit shows 3 or 5 vertical 

 ridges and a thin membranous margin. In the space between 

 every two ridges there is a dark mark which does not reach 

 the base of the half -fruit and is thickened at the lower end. 

 These marks are due to oil-containing cavities in the wall of 



