268 BOTANY. 



541. In the Compositse (Fig. 146) the five anthers are 

 united into a ring or tube around the style. The pollen 

 escapes from the inner side of the anthers into the anther- 

 tube, and at this time the immature style is short. As the 

 latter grows it pushes up through the anther-ring, carrying 

 the mass of pollen with it. Insects visiting the flowers for 

 nectar at this stage rub ofE the little piles of pollen from 

 the top of the stamen-tubes, and coming in contact after- 

 wards with the expanded stigmas of other flowers, some of 

 the pollen is left upon them. 



542. 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 Com- 

 posites, in addition to these structural peculiarities, the 

 stamens are sensitive, and when touched will suddenly 

 contract, drawing the anther-tube down and ejecting pol- 

 len. This may easily be seen by passing the finger quickly 

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



543. The foregoing must serve to direct the student to 

 the careful observation of the flowers 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 are likewise polli- 

 nated by insects. 



644. Among the interesting things to which attention 

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



