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 fiower. With 

 a needle any particular filament may be touched, and the movements to and 



Fig. 14. Leaf Ctiicus undttlattts sax. mesacephalus 



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 ihe anther ring down until the brush of hairs has passed 

 through, when the worii 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 



