237 



travel by boat a tedious and laborious process. Beds of lotus 

 {Neliimho Intea) and patches of Azolla will suggest warmer 

 climes, while the fields of rushes {Scirpus fluviatilis), and patch- 

 es of water-lilies {Nymphcea reniformis), arrowleaf {Sagittaria 

 variahiUs), and pickerel-weed [Pontederia cordata) will recall 

 familiar scenes in northern waters. The carpets of LemnacecB 

 will be surprising, and the gigantic growths of the semiaquatic 

 Polygonums will furnish evidence of the fertility of their en- 

 vironment. 



Both the nature and the quantity of the vegetation varies 

 in the different localities whose plankton has been the subject 

 of investigation by us, and in the same locality the conditions 

 may change at different seasons and from year to year, low 

 water in the early summer favoring its growth, and summer 

 floods and fishermen's seines uprooting and sweeping it away. 



The following list includes only the most common and 

 most important members of the aquatic flora, with brief notes 

 on their habitat and frequency. 



Ranunculus multlfidus Pursh. Found occasionally in quiet 

 waters in shoal regions with soft alluvial bottom. 



Caltha palustr'is L. Rare, along springy shores. 



Nelumbo liitea Pers. Forming large patches in the more 

 open vegetation in the permanent backwaters on very soft allu- 

 vial bottom. Usually at some distance from shore and in quiet 

 waters. 



Nymphcea reniformis D. C. Common in the more open 

 regions of the permanent backwaters in quiet regions, and along 

 channels on alluvial bottom. 



Cardamine rhomhoidea D. C. Rare, along springy margins. 



Cardamine hirsuta L. Occasional, along alluvial margins. 



Nasturtium sessiliflorum Nutt. • Rare, along wet sandy mar- 

 gins. 



Nasturtium palustre D. C. Common, in shallow water along 

 alluvial shores. 



Proserpi}iaca pjalustris h. Rare, along shady shores perma- 

 nently fed by springs. 



