280 BOTANY. 



wards with the expanded stigmas of other flowers, some of 

 the pollen is left upon them. 



529. After the pollen is set free the style elongates still 

 more, and finally the two lobes of the stigma open out and 

 are ready for pollination. This development takes place 

 beginning at the outer rows of flowers in each flower-head 

 and proceeds towards the centre. Thus at any time in 

 any blooming flower-head, as of the Sunflower, there may 

 be seen a ring of pollen-bearing flowers and outside of it a 

 ring of flowers with expanded stigmas. In some Compo- 

 sites, in addition to these structural peculiarities, the sta- 

 mens are sensitive, and when touched will suddenly con- 

 tract, drawing the anther-tube down and ejecting pollen. 

 This may easily be seen by passing the finger quickly across 

 the top of a thistle-head when in full bloom. 



530. The foregoing must serve to direct the student to 

 the careful observation of the fiowers of Dicotyledons. He 

 should remember Lubbock's remark that "it is probable 

 that all flowers which have an irregular corolla are polli- 

 nated by insects,'" and to this he may well add that it is 

 equally probable that all tubular flowers which open their 

 lobes are likewise pollinated by insects. 



531. Among the interesting things to which attention 

 has been directed during the past few years is that of the 

 insectivorous habits of certain plants. Here again no more 

 than a fragment can be given, barely enough to introduce 

 the student to the subject. 



532. Many plants catch insects by means of their sticky 

 glandular hairs, or glandular surfaces upon their stems or 

 leaves. This may be readily seen by examining a petunia- 

 or tomato-stem, or the sticky belts on the stems of various 

 species of Catchfly, or the sticky spots on the bracts sur- 



