IOWA ACADEMY OF SCIENCES. iOl 



bursting of the tubular corolla, the anther tube formed by the lateral union of the 

 five anthers and enclosing the stigma, is protruded, its entire length appearing 

 beyond the corolla tube. The anthers now dehisce liberating ^he stigma which 

 forcibly protrudes itself, at the same time recurving and carrying with it, lodged 

 in its papillose projections, numerous pollen grains. The filaments then retract 

 drawing the empty anther tube again within the corolla. Furthermore the disk 

 flowers open from circumference to center. Were the pollen of the outer row not 

 potent in the fertilization of its own stigma, it must be conceded to be entirely 

 useless so far as individual disks are concerned. Moreover, if the flowers at the 

 center of the disk which open after the retraction of the anther tubes in the outer 

 rows, were wholly dependent upon cross-fertilization, we might expect to find them 

 in many cases sterile. No evidence of such a condition occurs. Hence, we con- 

 clude from its complete mechanism and from results exhibited, that in the sun" 

 flower ample provision is made for self-fertilization. But the fact that the flower 

 is thus well equipped for its own perpetuity does not exclude the possibility of the 

 co-operation of outside agents. The evidences of cross-fertilization by means of 

 insects are equally numerous and conclusive. While the flowers around the border 

 are opening, the center of the disk, glabrous with odorous resin, is a favorite resort 

 for various H;/me>io2?tera. The nectar of the flower appears to be secreted at the 

 base of the corolla, where the style is attached. To reach the nectar it is not neces- 

 sary that the proboscis of the insect be inserted inside the anther tube. Hence, it 

 would seem at first thought quite probable that it might escape without carrying 

 any pollen. This may in some instances be true, but it is to be further noticed 

 that the slightest mechanical pressure at the base of the style, before dehiscence, 

 thrusts the stigma out with an explosive effect so that a bee entering the flower at 

 this point would be completely dusted with pollen. The complete exposure of the 

 stigmas of older flowers would insure the deposit of some of this pollen upon them 

 as the bee passes over. Furthermore, the fact of the legs of the insect being 

 sticky from the resin so abundant on the disk, together with the abundance of 

 pollen produced, would afford reasonable grounds for the conclusion that pollen is 

 thus transported. Actual observation confirms this view and it is a well known 

 fact that flowers of this family are subject to frequent visits from both nectar and 

 pollen gatherers. 



Sir John Lubbock in his "British Wild Flowers" shows the Composita' to be 

 specially adapted for fertilization by insects from the facts that (1) the heads are 

 conspicuous, (2) the honey easily obtained, and (3} the small size of the florets 

 insures the touchii-ig of many by one insect and hence effectual pollination. 



Hermann Mueller also recognizes this agency and notes the special modification 

 of certain parts in the insect for this purpose. 



It is not the purpose of this paper to furnish complete lists of the insects 

 which have been found on the species cited, but rather to point out some of those 

 most persistent about certain flowers and determine, if possible, something as to 

 their importance in pollination. 



On HeVmnthus annnus L. by far the most frequent visitor was the common honey 

 bee (A2)is melUjica). This was especially true of plants growing near hives of 

 bees, but was also true of plants observed in other localities. Bombiis Pentisyl- 

 vanicus was also a frequent visitor. It was sometimes found with its legs heavily 

 laden with pollen, but usually it was packed into a sort of wax. This was also 

 true, many times, of the honey bee, but in both cases loose pollen grains were 

 found scattered abundantly over the head and body of the insect, in a position to 

 be easily brushed off. Other visitors were Mellisodes obli(]uus. closely resembling 



