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NATURE-STUDY REVIEW [14:6— Sept. 1918 



of bracts, and is composed of two kinds of flowers. Those in the 

 center, called disk flowers are very small and have a five-lobed 

 tubular corolla fringed at the base with short white hairs. They 

 are sometimes bright yellow and sometimes orange red to purple 

 in color. They contain a pistil and five stamens. Surrounding 

 this central disk are the showy banner flowers whose corollas have 

 been prolonged into long tubes split down one side, making them 

 look like long banners. These are colored white, pink, pale 

 lavender to deep purple according to the species, and give to the 

 flower heads the peculiar star-like appearance that inspired the 

 scientists of old to call the flower "aster" which means a star. 



I, an aster flower-head enlarged; 2, a disk-flower; 3, a banner-flower 



Let us examine a disk-flower and see what provision the plant 

 makes for fertilization. In the center of the flower-head we find 

 the little flowers closed up tight, the tips of the five pointed corolla 

 tube meeting at the center. They look like little pentangular balls. 

 Towards the outer edge we find flowers at different stages of devel- 

 opment, those in full bloom at the outermost edge. Here we see 

 the aster's trick to prevent self-fertilization. 



The anthers are joined into a tube but the filaments are separate 

 and fastened to the corolla. The anthers split open lengthwise on 

 the inside of the tube. The pistil is two-branched and provided 

 with sweeping hairs like a duster. It pushes up through the 

 stamen-tube after the pollen is ripe and brushes the pollen out 

 before it, so that early in the morning, before the insects have 

 arrived, we can see little circles of pollen piled up around each 

 little floret of the aster head. The branches of the pistil do not 

 spread apart and expose the stigmatic surface until they have grown 



