128 THE STORY OF THE PLANTS. 



as shown in the figure, we often find a cup here 

 and there which contains both stamens and pistil 

 together. 



I have already told you that in many plants 

 the calyx helps the corolla as an advertisement 

 for insects ; and sometimes, as in the marsh- 

 marigold and the various anemones, where there 

 are no petals at all, it becomes so brilliant as to 

 be mistaken for petals by all but botanists. One 

 way in which such a substitution often happens 

 is shown us by the great burnet, which is a close 

 relation of the salad-burnet. This plant, after 

 having acquired the habit of wind-fertilisation, 

 has taken again at last to insect marriage. Hav- 

 ing lost its petals, however, it can't easily rede- 

 velop them ; so it has had instead to make its 

 calyx purple. The plant as a whole closely re- 

 sembles the salad-burnet ; but the flowers are 

 rather different ; the stamens no longer hang out 

 of the calyx; the calyx cup is more tubular; and 

 the stigma is shortened to a little sticky knob, 

 instead of being divided into feathery fringes. 

 These differences are all very characteristic of 

 the contrast between wind and insect-fertilisation. 



The common nettle supplies us with an excel- 

 lent example of another form of wind-fertilisa- 

 tion, carried to a still higher pitch of develop- 

 ment. Here the sexes grow on different plants, 

 and the flowers are tiny, green, and inconspicu- 

 ous. The males consist of a calyx of four sepals, 

 each sepal with a stamen curiously caught under 

 it during the immature stage. But as soon as they 

 ripen they burst out elastically, and shoot their 

 pollen into the air around them. In this case, 

 and in many like it, the plant itself helps the 

 wind, as it were, to disseminate its pollen. 



