15° 



DICOTYLEDONS 



comes a matter of difificulty to prove that there are five carpels. 

 The facts that the capsule opens by five double-teeth, and that 

 in " monstrous " flowers five leaves often replace the single 

 gynsecium, suggest that the gynaecium represents five carpels. 

 R:Tiit (fig. 189) a capsule dehiscing by five double-teeth. Seeds 

 shield-like in shape, endospermic. Pollination. — The flowers 

 of some Primrose plants have stamens inserted in the throat 

 ^j of the corolla, so that the five anthers form 

 a circle just within the mouth of the corolla- 

 tube ; in these flowers the style is short, 

 the stigma is hidden deep down in the 

 corolla-tube : this is the short-styled form of 

 flower (fig. 187, left-hand figure). In other 

 plants the relative positions of the anthers 

 and stigma are just reversed, and a long 

 style raises the stigma to the mouth of the 

 corolla-tube, whilst the shortness of the 

 filaments and their insertion lower down 

 the corolla-tube cause the anthers to be 

 hidden inside the tube : this is the long- 

 sty led form of flower (fig. 187, right-hand 

 figure). Comparing the two forms of 

 flowers, we see that the anthers of 

 one form stand at just the same level up the corolla-tube 

 as does the stigma of the other form (see fig. 187). Honey 

 is excreted by the base of the ovary. An insect with a 

 sufficiently long tongue, when it goes from one form of flower 

 to the other, will accurately transfer the pollen from the anthers 

 of the one on to the stigma of the other in each case, because 

 the pollen is deposited on a particular part of the insect's 

 tongue. Spontaneous self-pollination is possible in the short- 

 styled form. 



Fig. i8p. — Fruit of 

 Primrose. 



Type II. : POOR-MAN'S WEATHER-GLASS 

 (Anagallis aroensis). 



A small annual herb with red flowers. [There are very few 

 British plants with red flowers.] Flowers solitary in the leaf- 

 axils. The flowers are constructed on the same plan as in the 

 Primrose, but with a shortened tube : K5 C5 A5 G(5). There 



