CHAP, xxn WIND- AND INSECT-POLLINATION 99 



(r) Is this protogyny or protandry? 



8. Heterostyfy. 



(a) Examine flowers of a number of different plants of 

 the Bluet (Houstonia coerulea) or of some species 

 of Primrose, and notice : 



1. The fact that some flowers have long styles and stamens 



inserted about half-way up the tube of the corolla, 

 while 



2. Others have short styles and the stamens inserted near 



the top of the tube of the corolla. 



3. Explain, if you can, how this structure serves the same 



purpose as a separation of the sexes in these flowers. 



4. (Examine, also, the stigmas and pollen of both kinds 



of flowers under the compound microscope.) 



9. Examine the Purple Loosestrife (Ly thrum Salicaria) 



or the Swamp Loosestrife (Nesaa or Decodoti) in the 

 same way, and notice that there are three kinds of 

 flowers, representing three lengths of filament and 

 three lengths of styles. What is the use of this ? 

 10. Examine flowers from a number of plants of Esch- 



scholtzia and notice : 



(a) The fact that in some flowers two of the four styles 

 are longer than the other two. What advantage 

 does the plant derive from this ? 



