IOWA ACADEMY OF SCIENCES. 
221 
the style and falls out into the vacant space in the anther tube above the tip 
of the style. The upper end of the anther tube opens easily, and any 
mechanism that will either raise the style or draw down the anther tube 
would cause the pollen to pass out this terminal pore. The latter method is 
observed in the thistle. When the conditions are favorable the filaments 
contract quickly. It frequently occurs that the five filaments do not act at 
the same time, and this causes the noticeable swaying of the flower. With 
a needle any particular filament may be touched, and the movements to and 
Fig. 14. Leaf Cnicus undulatus \ ar. megacefihalus 
fro of the flower governed at pleasure, until the stimulus is transmitted to 
the other filaments, when the swaying ceases. During this time the anther 
tube has descended two or three millimetres and a quantity of pollen is 
pushed out of the pore by the protruding style. The filaments soon read- 
just themselves and succeeding touches of the flowers by insects or other- 
wise will bring the anther ring down until the brush of hairs has passed 
through, when the work of the sensitive structures is accomplished. The 
style may now elongate, but its surface is smooth from the base of the brush 
or rosette of stiff hairs, down to its insertion. The two unequal halves of 
the upper end of the style were not found separated from each other in any 
of the hundreds examined. There is a deep suture between the two parts 
near the tip and along this the pollen adheres and germinates. Some 
observations were made upon the .rate of opening of the blossoms in a head. 
For this purpose heads nearly ready to bloom were placed in water out of 
the reach of insects. In one head some of the outer flowers were only partly 
open in the morning. On the evening of the same day one hundred flowers 
had their anther tubes drawn back and their pollen in sight. The next 
morning a string was placed between the old flowers and a circle of 
younger ones that were rising. That evening seventy-four more flowers 
were in full bloom. A second string was placed around the last circle of 
flowers. On the third morning fifty-five flowers had their corollas raised 
above the level of the inner portion of the head. Flowers that are to open 
upon any day push up about a half inch above their younger associates, in 
the head, on the previous night. The flowering in a head lasts about a 
week, the number of blossoms opening daily diminishing from the first day 
of general blooming. It often occurs that only a few scattered outside 
flowers will bloom the first day. In such cases the next day is the first of 
general blooming, when a hundred or more flowers unfold. 
The style lengthens and protrudes much beyond the sta- 
mens. In the proterandrous stage of course the style is 
