HOW PLANTS MARRY. 83 



cured. The first of these sets of organs, going 

 still from within outward, is called \.\\z petals, or, 

 collectively, the corolla. Sometimes, as in the 

 dog-rose or the buttercup, the corolla consists of 

 five separate petals ; sometimes, as in the harebell 

 and the gentian, it has five points, or lobes, united 

 at the base into a single piece (Fig. 17). Last of 

 all, outside the corolla again comes another row 

 or layer, called the calyx, which sometimes con- 

 sists of five separate leaves or sepals, as in the 

 dog-rose and the buttercup, but sometimes has 

 five points, welded at the base into one piece, as 

 in red campion and convolvulus. It is these last 

 comparatively unessential but very conspicuous 

 parts that most people think of when they say 

 " a flower." 



What is their use? Well, they are not essen- 

 tial, like the pistil and stamens, because many 

 flowers, perhaps even most flowers, do without 

 them altogether. But they are very useful for 

 all that, as we may easily guess, because they are 

 found in almost all the most advanced and devel- 

 oped flowers. The use of the corolla, with its bril- 

 liantly coloured petals, is to attract insects to the 

 flowers and induce them to carry pollen from 

 plant to plant. That is why they are painted red 

 and blue and yellow; they are there as advertise- 

 ments to tell the bee or butterfly, " Here you can 

 get good honey." The use of the calyx is usually 

 to cover up the flower in the bud, to keep it safe 

 from cold, and to protect it from the attacks of 

 insect enemies, who often try to break through 

 and steal the half-developed pollen in the bags of 

 the stamens before it is ripe and ready for fer- 

 tilising. These are the chief uses of the calyx or 



