564 EEPOET OF STATE GEOLOGIST. 



It is in these areas of over-lap and changing conditions that those 

 variations from "the description" are constantly occurring, which are 

 responsible for so many errors of reference in plant lists. The plasti- 

 city of the plant and the potency of environmental factors have been 

 too often lost sight of by the systematise 



HYDKOPHYTES. 



The following plants may be taken as the most prominent forms of 

 this type. The distribution of the species will be found in the general 

 catalogue: 



Typha latifolia L. Cat-tail. 



Potamogeton pulcher Tuckerm. Pondweed. 



Potamogeton prcelongus Wulf. Pondweed. 



Potamogeton zosterafolius Schum. Pondweed. 



Potamogeton foliosus Raf. (== P. pauciflorus Pursh.). 



Potamogeton diversifolius Raf. (= P. hybridus Michx.). 



Potamogeton Spirillus Tuckerm. 



Potamogeton Robbinsii Oakes. 



Zannichellia palustris L. Horned Pondweed. 



Sagittaria latifolia Willd. (= S. variabilis Engl.). Arrowhead. 



Philotria Canadensis (Michx.) Britt. (= Elodea Canadensis Michx. ). 



Waterweed. 

 Vallisneria spiralis L. Tape-grass. Eel-grass. 

 Alisma Plantago-aquatica L. (= A. Plantago L.). Water Plantain. 

 Eriocaidon septangulare Withering. Pipewort. 

 Wolffia Columbiana Karsten. 

 Spirodda polyrhiza Schleid. 

 Lemna trisulca L. Duckw T eed. 

 Lemna minor L. 



Peltandra Virginica (L.) Kunth. Arrow Arum. 

 Pontederia cor data L. Pickerel- weed. 

 Heteranthera reniformis Ruiz, and Pav. Mud-plantain. 

 Heteranthera dubia (Jacq.) McM. (= H. graminea Vahl.). 

 Iris versicolor L. Larger Blue Flag. 



Polygonum Harturightii Gray. Knotweed. Red-flowered Smartweed. 

 Polygonum hydropiperoides Michx. 

 Polygonum amphibium L. Water Smartweed. 

 Ceratophyllum demersum L. Hornwort. 

 Cabomba Caroliniana Gray. 



Brasenia purpurea (Michx.) Casp. (= B. peltata Pursh.). Watershield. 

 Nymphaxi advena Soland (= Nuphar advena Ait.). Yellow Pond Lily. 



Splatter Dock. 



