206 
THE LIFE OF FLOWERING PLANTS 
Show how the pistil, with its stigmatic surfaces pressed tightly together, 
pushes up through the pollen which fills the tube, becoming covered on 
the outside. Show mature pistil with expanded stigma. If possible 
show dandelions with insects on them. What 
are the insects doing? What happens to the 
pollen ? 
Pollen grains. — Place a few, preferably large 
ones, on a slide; cover with 5 per cent sugar 
solution; put under a bell jar and set in a warm 
place for half an hour. Then add a cover glass 
and examine for pollen tubes. Examinations 
may be repeated at intervals for a number of 
hours. 
Carefully split the style of a large flower, like a 
lily, noting the passage in the middle for the pollen 
Figure 190. — Disk tubes. If the pistil has not a tubular center, 
Flower of Daisy. what is the character of the tissue in the center? 
190. Composite Flowers. — These flowers are closely 
crowded or grouped into a head, on a common receptacle. 
Such is the dandelion or the daisy, each 
group being commonly called a flower. 
Two lands of flowers are to be found in 
these heads, tubular flowers, that is, with 
the corolla a tube, and strap-shaped flowers 
in which the corolla is long and slender. 
Some composite flowers, like the dande¬ 
lion, have only the strap-shaped, and 
others, like the thistle, only the tubular 
kind. Still others, like the common daisy 
and the sunflower, have both kinds. In 
the daisy, the tubular flowers, found only 
in the middle, are called disk flowers. 
These make up the yellow part of the 
group. Outside of them are the white 
strap-shaped kind, known as the ray 
flowers. In the sunflower the disk flowers are brown, and 
the ray flowers yellow. Many other combinations occur. 
Figure 191. — Ray 
Flower of Daisy. 
