46 



NATURAL HISTORY BULLETIN 



trichioides Casp., as having a filiform axis to the stauiinate flow- 

 er, but no similar structures seem to have been noted among our 

 members of this genus. Accordingly the plants above noted were 

 studied with care, and observations were continued through the 

 two succeeding summers. 



The plants under discussion were large and vigorous, and 

 flourished abundantly in the north end of East Okoboji lake, at 

 times completely dominating certain areas. Every one of the 

 hundreds of staminate flowers examined displayed the same trait, 

 seeming to point to a distinct strain of these plants in that lo- 

 cality. During the summer of 1910 these plants were found in 

 the same place and also at another point in the lake four miles 

 distant. The low water prevailing in these lakes during the 

 summer of 1911 greatly altered the number and distribution of 

 water plants but the form in question was fairly abundant. The 

 associated pistillate plants, whose flowers closely resemble those 

 of the common species, were abundant and set seeds regularly. 

 In all this time the other form, E. canadensis Michx. was not 

 noted in the waters of these connected lakes. 



The lower portion of the spathe of these pollen bearing flowers 

 is early constricted (Pig. 3), and might resemble in a superficial 

 way the condition described as "spathe peduncled" by Rydberg^ 

 in his description of Philotria linearis Rydb. and P. Planchonii 

 (Casp.) Rydb., though the spathe of our form is strictly sessile. 

 The outer end of the spathe expands abruptly into a flattened 

 two-cleft circular portion which loosely invests the body of the 

 flower which is pedieillate within the spathe. 



At maturity the axis elongates rapidly, pushing the flower out 

 of the spathe (Fig. 2), and outward into the water when its 

 buoyancy carries it upward toward the surface. The degree of 

 elongation of the axis is related in a general way to depth of its 

 insertion. Those borne near the surface may be but two or three 

 centimeters in length, while those in deeper water show extreme 

 elongation. Specimens were measured in 1911 28 cm. long and 

 no doubt this did not represent the extreme of elongation. 



The staminate flower is thus carried up on a slender whitish 

 thread which resembles in a superficial way the "floral tube" of 

 the pistillate flower. In Caspary's descriptions the same term, 

 ^' tubus calicis, " is applied to both of these elongated structures. 



^ Rydberg, P. A., Flora of North America. 



