IOWA ACADEMY OF SCIENCE 67 



out further consideration, since it is unthinkable that these rudimentary 

 parts are present in anticipation of a bisporangiate condition. Assum- 

 ing, then, that the rudimentary structures are the vistages of once func- 

 tional organs, we must assume for these plants an ancestry with perfect 

 flowers. Why, then, are they shifting to the monosiDorangiate condition? 



This species has, no doubt, made the shift from land to water quite 

 recently. This transition must always be accompanied by great changes 

 in the structures and habits of a plant. Vegetatively, Myriophyllum 

 has solved this problem and adjusted itself admirably to its new environ- 

 ment, as is true of many other aquatic plants. But the problem of repro- 

 duction by seeds seems to present more serious difficulties, and it is 

 probable that the change from perfect to monosporangiate flowers may 

 be an attempt on the part of this plant to favor its pollination. A few 

 aquatic plants, such as Ceratopkylhim demersum L.^ have developed 

 structures whereby pollination may take place underneath the surface 

 of the water. On the other hand, the great majority of aquatic seed 

 plants must bring their flowers to the surface for pollination. A few 

 such plants, as the potamogetons, have perfect flowers, but there seems 

 to be a strong tendency toward the separation of the flowers in such 

 habitats. ZannicJiellia and Zostera are monosporangiate and monoe- 

 cious, while Elodea, Vallisneria, Najas, and other aquatic seed plants, 

 have gone a step further and are monosporangiate and dioecious. In 

 some of these, the shift from perfect flowers has been made quite rec- 

 ently. Wylie' in his study of Elodea caudeoisis ]\Iiehx, has come to 

 this conclusion in regard to that plant, as he finds rudiments of the sup- 

 pressed parts always present. No doubt such rudiments are more com- 

 mon than now recognized among the other genera. Thus, there seems 

 to be a broad tendency toward the monosporangiate habit among these 

 water plants. IMyriophyllum may be considered in line with this ten- 

 dency, though the advantages of the habit to this species are not clear. 

 Since the order of inflorescence is acropetal and the pistillate flowers 

 open before the pollen of the same spike matures, self-pollination would 

 be ruled out. Long continued study of this plant afforded no evidence 

 of insect pollination. The separation of the spikes, and their slight ele- 

 vation above the water would not especially favor wind pollination. It 

 may be, however, that floating pollen, driven by the wind, plays an im- 

 portant part, in which ease, there would be a decided advantage in hav- 



6. Strasburger. E. Ein Beitrag zur Kenntniss von Ceratophyllum submersum 

 und Phylogenetische Erorterungen. .lahrb. Wiss. Bot. ?>7:477-52G, 1902. 



7. Wylie, R. B. The Morphology of Elodea canadensis. Bot. Gazette 37; 1- 

 22, 1904. 



