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A TEXTBOOK OF THEORETICAL BOTANY 



possess no stamens, the corolla is tubular and slender while the style is 

 filiform and smooth. The tip of the style branches, the outer surface being 

 beset with fine hairs, the inner surface of the branches with papillae. The 

 pollen grains are white, roundish bodies with long spines adapted to secure 

 adhesion on the stigmatic papillae. The flowers are visited mainly by bees. 



In Petasites hybridus (Butterbur) the plants are completely unisexual, 

 the male being much the commoner. 



Turning to the Astereae we may cite the common Michaelmas Daisy as 

 an example (Fig. 1889). The female ray florets are brightly coloured, either 

 red or blue, while the disc florets are yellow and hermaphrodite. These 

 latter florets have corollas in which the lower portion is contracted and 



wm 



B 



Fig. 1889. — Aster nori-belgii. Michael- 

 mas Daisy. A, Pollen mass being 

 extruded from the anther tube by 

 upgrowth of the style. B, Later 

 stage, with emergent style with two 

 stigmatic lobes, each ending in a 

 mass of sweeping hairs to which a 

 few pollen grains still adhere. 



stalklike while the upper portion is expanded into a bell. The pollen is 

 swept out by the lips of the stylar branches which are beset with upwardly 

 projecting sweeping hairs. When the anther cylinder is empty the style 

 projects well above the rest of the inflorescence. At this stage the lips of 

 the styles remain closed together and therefore an insect visiting the flower 

 at this stage will become dusted with pollen. Later the stigma opens and 

 exposes the stigmatic papillae, so that when a flower in this stage is visited 

 by an insect bearing pollen, the grains are distributed on the receptive 

 surface. Automatic self-pollination is also possible on account of pollen 

 left on the stylar hairs. The flowers are visited by various kinds of insects, 

 flies, bees and butterflies, the latter being the most common late in the 



