237 
travel by boat a tedious and laborious process. Beds of lotus 
(Nelumbo lutea) and patches of <Azolla will suggest warmer 
climes, while the fields of rushes (Scirpus fluviatilis), and patch- 
es of water-lilies (Nymphwa reniformis), arrowleaf (Sagittaria 
variabilis), and pickerel-weed (Pontederia cordata) will recall 
familiar scenes in northern waters. The carpets of Lemnacee 
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 multifidus Pursh. Found occasionally in quiet 
waters in shoal regions with soft alluvial bottom. 
Caltha palustris L. Rare, along springy shores. 
Nelumbo lutea 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. 
Nymphea reniformis D.C. Common in the more open 
regions of the permanent backwaters in quiet regions, and along 
channels on alluvial bottom. 
Cardamine rhomboidea 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. 
Proserpinaca palustris L. Rare, along shady shores perma- 
nently fed by springs, 
