HOW TO STUDY PLANT LIFE 77 



collectively the involucre (see p. 162). Pull 

 off several bracts so that you may remove a 

 few ray flowers, or florets, easily and without 

 injury. The corolla is strap-shaped for half 

 of its length (Fig. 4), but near the middle its 

 edges unite to form a tube. This is sur- 

 rounded by a ring of long hairs which grow 

 from its base the strangely transformed calyx 

 of the floret. From the tube peeps the tiny 

 pistil with its two branches, or arms, called 

 stigmas. There are no stamens, so these 

 purple ray florets are imperfect and cannot of 

 themselves produce seed. You will probably 

 ask why they should exist ; but imagine how in- 

 significant and unattractive the flower-head 

 would look without them. They are not use- 

 less, for even though they should not produce 

 seed, they attract insects to the seed-producing 

 yellow florets of the disc. They act as flags, 

 and so serve a most useful purpose. 



Some plants are fertilized by their own 

 pollen, others either occasionally or invariably 

 require pollen from other flowers of the same 

 species before good seed can be set. This pol- 

 len is conveyed from plant to plant chiefly 



