THE FLOWERS OF MYRIOPYHYLLUM SPICATUM L. 



BY N. D. KNUPP. 



The Myrtales comprise one of the highest orders of the Archichla- 

 mydeae. They are characterized by the adhesion of calyx and recep- 

 tacle, usually epigynous, always cyclic, with a definite number of parts 

 in each whorl. The order is an important tropical one, and furnishes 

 many products of commercial value. More recently the group has at- 

 tracted widespread attention as it contains the genus Oenothera with 

 which De Vries worked out his mutation theory. 



]\Iyriophyllum falls in a subdivision of this order, the Haloragi- 

 daceae, a small family of aquatic and marsh plants. There is an 

 added interest in this family on account of its belonging to that as- 

 semblage of land plants which have adapted themselves to an aquatic 

 habitat. It was primarily on this account that this study was under- 

 taken. 



To Dr. R. B. Wylie, under whose direction and guidance this work 

 was carried on, I feel greatly indebted for his encouragement and as- 

 sistance. My thanks are also due Professor Maebride for his helpful 

 interest and numerous courtesies. 



Methods. 



The material for this study was collected during the summers of 

 1909 and 1910 at the Iowa Lakeside Laboratory on Lake Okoboji. It 

 was killed in 1% chromo-acetic acid and preserved in 70% alcohol. 

 Later it was embedded in paraffin and serial sections cut on the micro- 

 tome from 6 to 13 microms in thickness. The stains used were Dela- 

 field's Haematoxylin, Iron-alum Haematoxylin, and Flemming's Triple 

 stain. 



MyriophyUum spicatum L. is an aquatic seed plant, living com- 

 pletely submersed during its vegetative existence, only the flowers ap- 

 pearing above the surface of the water. It grows very abundantly in 

 some of the bays and shallower parts of Lake Okoboji. A small bay 

 of about 10 acres near the Lakeside Laboratory, ranging in depth from 

 3 to 10 feet, was practically filled with aquatic plants, a large proper- 



