50 



NATUEAL HISTOEY BULLETIN 



scheint sich nicht lozulosen. Die Spatha der mannlichen Bliithe 

 ist lineal-cylindrisch. " The slender spathe would seem to be a 

 point in evidence also of the homology of these structures, — in 

 which ease there can be no agreement with our form. But as- 

 suming the term "tubus calicis" of these descriptions relates to 

 the peduncle of the staminate flower there are many points of 

 difference between any of them and the Okoboji plant. In addi- 

 tion, the wide geographical separation, — in opposite hemispheres, 

 — would suggest caution in correlating these forms, though 

 Caspary** refers to at least three species that are dioecious and 

 may have peduncled staminate flowers {Elodea chilensis Casp., 

 Elodea callitricliiodes Casp., and Elodea Najas Casp.) that offer 

 similarities to the form in question. 



The occurrence of the plant under discussion in the waters of 

 the Okoboji lakes suggests two alternatives; — Either, (1) that it 

 is a form of local development, with perhaps a limited range, or, 

 (2) that it belongs to a species of possibly wide distribution to 

 the west and northwest of the ^Mississippi basin which has not 

 yet been clearly identified nor fully described. 



Favoring the former view is the considerable depth of these 

 Okoboji lakes (over 100 feet in places), thus pointing to a prob- 

 ably constant body of water since the last glacial invasion, — 

 the lakes having been formed in part at least by the Wisconsin 

 ice-sheet. These quiet waters, through thousands of years, hav- 

 ing at all times shallower margins favoring the growth of such 

 plants, would have made ready the stage for possible mutations. 



Favoring the latter alternative, which to the writer seems 

 probable, is the relative inconspicuousness of the flowers sug- 

 gesting that this form might easily have escaped the casual 

 observer. Jn its younger stages it is not strikingly different from 

 the common species, while in its maturity the flower resembles 

 the pistillate flower in a general way. Of course no skilled col- 

 lector would be deceived, but when one recalls the relative in- 

 accessibility of these plants to the pedestrian collectors, and the 

 greater interest of most pioneer workers in the more conspicuous 

 land plants, one is inclined to the view that this form may be 

 found more generally in the lakes to the west and northwest as 

 these are studied more thoroughly. 



^ Loc. cit., 469-477. 



