522 BOTANICAL GAZETTE _ UNE 
In comparing the mountain lakes with those of the plains and 
lower altitudes generally, it is striking that those of lower elevations 
support the richer aquatic vegetation. The ponds of Boulder 
Park do not have many species commonly known as belonging to 
the water habitat. For example, there will be noted the total 
absence of species of Lemna, Hydrocharis, Ceratophyllum, Utri- 
cularia, Riccia, Azolla, and Salvinia, free floating species common at 
lower altitudes. Of these, several Lemna spp. and Utricularia 
vulgaris have been collected at elevations in Colorado as high as 
Boulder Park. Many submersed and emersed fixed species are not 
to be found here. Among such may be mentioned species of Nitella, 
Tsoetes, Naias, Elodea, Nymphaea, and a number of Potamogeton 
spp. Several other species of Potamogeton, Nymphaea polysepala 
(Engelm.) Greene, Isoetes Bolanderi Engelm., I. paupercula 
(Engelm.) A. A. Eaton, and Naias gaudalupensis (Spreng.) Morong 
are reported from a few lower altitudes in Colorado. 
The scarcity of aquatic plant life in the lakes and ponds of the 
Park is in part due to the coldness of the waters during a consider- 
able portion of the year. Moreover, the marsh type of vegetation 
here is meager, and little shelter is offered to many free floating 
forms. The lakes and ponds in Boulder Park contain very soft 
water. No doubt the same is true of most high altitude lakes. 
Nearly all plains lakes, however, are rich in alkali salts; bicar- 
bonates of calcium and magnesium, also of potassium and sodium, 
are quite universally present. A number of workers (2, 5, 25) have 
noted that waters rich in lime carbonates have a richer aquatic 
flora and fauna than soft waters. In the absence of free carbon 
dioxide, water plants may make use of the half-bound carbon 
dioxide of bicarbonates, chiefly those of calcium and magnesium, 
dissolved in the water. Undoubtedly the kind and quantity of 
dissolved salts in lake waters is an important factor in controlling 
vegetative development. In Boulder Park lakes and ponds the 
absence of these salts is quite likely a most important factor limiting 
the growth of algae and other submerged aquatics. 
The total absence of Scirpus, Typha, and Phragmites reed 
swamps in Boulder Park will be noted. 
