FERTILIZATION. 173 



ing essential organs of two forms, Fig. 157. Such flowers 

 are said to be dimorphous {of-tioo-forms). In the short-styled 

 flowers, I, II, the anthers are borne at the top of the corolla 

 tube a, S, and the stigma, g, stands about half-way up the 

 tube. In the long-styled flowers. III, IV, the stigma G is at 

 the top of the tube and the anthers, S, are borne about half- 

 way up. An insect, pressing its head into the throat of the 

 corolla of I or II would become dnsted with pollen which 

 would be brushed off on the stigma of a flower like III or IV. 

 On leaving' a long-styled flower, IV, the bee's tongue would 

 be dusted over with pollen, some of which would necessarily 

 be rubbed off on the stigma of the next short-styled flower 

 that was visited. Cross-fertilization is insured, since all the 

 flowers on a plant are of one kind, either long-styled or short- 

 styled, and since the pollen is of two sorts, each kind sterile 

 on the stigma of any flower of similar form to that from 

 which it came. 



Trimorphous 'flowers, with long, medium, and short styles, 

 are found in a species of loosestrife.* 



211. Studies in Insect Fertilization. — The student cannot- gather 

 more than a very imperfect knowledge of the details of cross-fertilization 

 in flowers without actually watching some of them as they grow, and 

 observing their insect-visitors. If the latter are caught and dropped into 

 a wide-mouthed stoppered hottle containing a bit of cotton saturated 

 with chloroform, they will be painlessly killed and most of them may be 

 identified by any one who is familiar with our common insects. The 

 insects may be observed and classified in a general way into butterflies, 

 motlis, bees, flies, wasps, and beetles, without being captured or 

 molested. 



Whether these out-of-door studies are made or not, several flowers 

 should be carefully examined and described as regards their arrange- 

 ments for attracting and utilizing insect-visitors (or birds). The following 

 list includes a considerable number of the most accessible flowers of 

 spring and early summer, about which it is easy to get information from 

 books. 



> See Miss Newell's Eeader in Botany, Part II, pp. 60-63. 



