230 STUDY OF COMMON PLANTS. 



retinacula, and leaving the pollen masses in the stigmatic 

 chamber, while it proceeds to other flowers and continues 

 gathering honey. 



Weaker insects are frequently unable to break the 

 retinacula. Flies may often be seen making unavailing 

 efforts to extricate themselves, and honey-bees are not 

 infrequently found that have been caught in the same 

 way, and have died after prolonged struggles to get free. 



By means of the preceding description, accompanied by 

 careful observation at each step, the student will be in a 

 position to study the entire mechanism to advantage. He 

 should now go over the whole independently, until every 

 part of the flower is perfectly familiar. The study of 

 external structure should be followed by a comparison 

 of cross and longitudinal sections (best made from alco- 

 holic material), with sketches to show the parts and their 

 relations to each other. 



Several hours will be required to do this properly. 

 Miiller's drawings may be consulted, but they are less 

 easily understood than the flower itself. Nothing can 

 possibly take the place of direct, personal, and long-con- 

 tinued study of the object under investigation. Further, 

 it is very desirable that the pupil should not only under- 

 stand the mechanism, but that he should also see it in 

 operation. A few days in summer spent in watching the 

 flowers of the milkweed, as the visitors come and go, will 

 give full opportunity for this. 



RELATIONSHIP. 



The Asclepiadaceae constitute a large and very remark- 

 able family of plants, including about thirteen hundred 

 species, which are largely tropical, although many repre- 



